pep8 fixes

- B007 Loop control variable not used within the loop body. If this is intended, start the name with an underscore.
    * modoboa/admin/lib.py
    * modoboa/admin/templatetags/admin_tags.py
    * modoboa/admin/tests/test_account.py
    * modoboa/admin/views/domain.py
    * modoboa/admin/views/identity.py
    * modoboa/core/views/dashboard.py
    * modoboa/limits/forms.py
    * modoboa/limits/handlers.py
    * modoboa/limits/tests/test_api.py
    * modoboa/limits/tests/test_domain_limits.py
    * modoboa/limits/tests/test_import.py
    * modoboa/limits/tests/test_user_limits.py
    * modoboa/limits/utils.py
    * modoboa/parameters/tools.py
    * modoboa/relaydomains/tests.py
- C402 Unnecessary generator - rewrite as a dict comprehension.
    * modoboa/admin/models/domain.py
    * modoboa/admin/views/domain.py
    * modoboa/admin/views/identity.py
    * modoboa/limits/searializers.py
- C407 Unnecessary list comprehension - can take a generator.
    * modoboa/core/password_validation.py
    * modoboa/parameters/tools.py
    * modoboa/transport/backends.py
- C408 Unnecessary dict call - rewrite as a literal.
    * modoboa/admin/tests/test_account.py
    * modoboa/admin/tests/test_alias.py
    * modoboa/admin/tests/test_password_schemes.py
    * modoboa/admin/views/domain.py
    * modoboa/admin/views/identity.py
    * modoboa/core/extensions.py
    * modoboa/lib/middleware.py
    * modoboa/lib/templatetags/form_tags.py
    * modoboa/lib/templatetags/lib_tags.py
    * modoboa/lib/web_utils.py
    * modoboa/limits/handlers.py
    * modoboa/limits/tests/test_user_limits.py
- E741 ambiguous variable name
    * modoboa/core/management/commands/cleanlogs.py
    * modoboa/limits/forms.py
    * modoboa/limits/tests/test_user_limits.py
    * modoboa/limits/utils.py
    * modoboa/relaydomains/tests.py
- F401 imported but unused
    * doc/conf.py
    * modoboa/admin/views/domain.py
    * modoboa/core/app_settings.py
    * modoboa/core/management/commands/load_initial_data.py
- F821 undefined name 'raw_input'
    * modoboa/core/commands/deploy.py
- F841 local variable 'test' is assigned to but never used
    * modoboa/core/app_settings.py
- N802 function name 'setUpTestData' should be lowercase xxx
    * modoboa/lib/email_utils.py - __ for name mangeling, _ for internal
- N805 first argument of a method should be named 'self'
    * modoboa/lib/connections.py
    * modoboa/lib/singleton.py

Ignore the following
- A001 "copyright" is a python builtin and is being shadowed, consider renaming the variable
    * doc/conf.py
- A003 is a python builtin, consider renaming the class attribute
    * modoboa/admin/factories.py
    * modoboa/admin/forms/domain.py
    * modoboa/admin/management/commands/handle_mailbox_operations.py
    * modoboa/admin/management/commands/modo.py
    * modoboa/admin/management/commands/subcommands/_repair.py
    * modoboa/admin/models/domain.py
    * modoboa/admin/models/mailbox.py
    * modoboa/core/commands/__init__.py
    * modoboa/core/commands/deploy.py
    * modoboa/core/commands/help.py
    * modoboa/core/management/commands/clean_inactive_accounts.py
    * modoboa/core/management/commands/cleanlogs.py
    * modoboa/core/management/commands/communicate_with_public_api.py
    * modoboa/core/management/commands/generate_postfix_maps.py
    * modoboa/core/management/commands/load_initial_data.py
    * modoboa/core/management/commands/set_default_site.py
- F401 imported but unused
    * modoboa/admin/apps.py - used to load handlers
    * modoboa/core/password_hashers/__init__.py - dynamically loaded
    * modoboa/limits/apps.py - used to load handlers
    * modoboa/relaydomains/apps.py - used to load handlers
    * modoboa/transport/apps.py - used to load handlers
- N802 function name should be lowercase xxx
    * modoboa/admin/tests/test_account.py
    * modoboa/admin/tests/test_alias.py
    * modoboa/admin/tests/test_domain_alias.py
    * modoboa/admin/tests/test_export.py
    * modoboa/admin/tests/test_mailbox_operations.py
    * modoboa/admin/tests/test_password_schemas.py
    * modoboa/admin/tests/test_repair.py
    * modoboa/core/tests/test_authentication.py
    * modoboa/core/tests/test_core.py
    * modoboa/core/tests/test_ldap.py
    * modoboa/core/tests/test_views.py
    * modoboa/lib/imap_utf7.py
    * modoboa/limits/tests/test_api.py
    * modoboa/limits/tests/test_domain_limits.py
    * modoboa/limits/tests/test_import.py
    * modoboa/limits/tests/test_user_limits.py
    * modoboa/relaydomains/tests.py

other fixes:
- use isinstance() instead of type() == Class

doc/conf.py

@@ -12,7 +12,7 @@
 # serve to show the default.
 
 import os
-import sys
+# import sys
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -44,7 +44,7 @@ master_doc = "index"
 
 # General information about the project.
 project = u'Modoboa'
-copyright = u'2018, Antoine Nguyen'
+copyright = u'2018, Antoine Nguyen'  # NOQA:A001
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the