Added French localization (#290)

* Initial commit of French localization

* Added French

* Changed translation for view key to stick to the one used in Moneropedia

lib/entities/language_service.dart

@@ -7,6 +7,7 @@ class LanguageService {
     'en': 'English',
     'de': 'Deutsch (German)',
     'es': 'Español (Spanish)',
+    'fr': 'Français (French)',
     'hi': 'हिंदी (Hindi)',
     'ja': '日本 (Japanese)',
     'ko': '한국어 (Korean)',

lib/utils/language_list.dart

@@ -2,6 +2,7 @@ class LanguageList {
   static const english = 'English';
   static const chineseSimplified = 'Chinese (simplified)';
   static const dutch = 'Dutch';
+  static const french = 'French';
   static const german = 'German';
   static const japanese = 'Japanese';
   static const portuguese = 'Portuguese';