API Lifecycle Implementation, Part 2 (#217)

* additon of 'get_mnemonic' API function

* rustfmt

* added 'change_password' api function

* rustfmt

* add 'delete_wallet' function'

* rustfmt

tests/data/v3_reqs/change_password.req.json

@@ -0,0 +1,10 @@
+{
+	"jsonrpc": "2.0",
+	"method": "change_password",
+	"params": {
+		"name": null,
+		"old": "passwoid",
+		"new": "password"
+	},
+	"id": 1
+}

tests/data/v3_reqs/create_wallet.req.json

@@ -4,7 +4,7 @@
 	"params": {
 		"name": null,
 		"mnemonic": null,
-		"mnemonic_length": 0,
+		"mnemonic_length": 32,
 		"password": "passwoid"
 	},
 	"id": 1

tests/data/v3_reqs/delete_wallet.req.json

@@ -0,0 +1,8 @@
+{
+	"jsonrpc": "2.0",
+	"method": "delete_wallet",
+	"params": {
+		"name": null
+	},
+	"id": 1
+}