PLT-3633 EE: Add Google and Office365 SSO through OAuth2 (#3660)

* EE: Add Google and Office365 SSO through OAuth2

* Add localization strings

* Text tweaks for PLT-3633

* Added sign-up button for Office 365

* Updated some error messages and a bit of licensing

* Updated sign-in method section in user settings to include Google and Office365

* Added more localization strings

config/config.json

@@ -142,10 +142,19 @@
         "Enable": false,
         "Secret": "",
         "Id": "",
-        "Scope": "",
-        "AuthEndpoint": "",
-        "TokenEndpoint": "",
-        "UserApiEndpoint": ""
+        "Scope": "profile email",
+        "AuthEndpoint": "https://accounts.google.com/o/oauth2/v2/auth",
+        "TokenEndpoint": "https://www.googleapis.com/oauth2/v4/token",
+        "UserApiEndpoint": "https://www.googleapis.com/plus/v1/people/me"
+    },
+    "Office365Settings": {
+        "Enable": false,
+        "Secret": "",
+        "Id": "",
+        "Scope": "User.Read",
+        "AuthEndpoint": "https://login.microsoftonline.com/common/oauth2/v2.0/authorize",
+        "TokenEndpoint": "https://login.microsoftonline.com/common/oauth2/v2.0/token",
+        "UserApiEndpoint": "https://graph.microsoft.com/v1.0/me"
     },
     "LdapSettings": {
         "Enable": false,
@@ -201,4 +210,4 @@
         "AndroidAppDownloadLink": "https://about.mattermost.com/mattermost-android-app/",
         "IosAppDownloadLink": "https://about.mattermost.com/mattermost-ios-app/"
     }
-}
+}