Add support for scope and add some missing translations

See this post on meta about the need for the ability to request a custom
scope:

https://meta.discourse.org/t/oauth2-basic-support/33879/116?u=blake

config/locales/server.en.yml

@@ -12,8 +12,11 @@ en:
     oauth2_json_username_path: 'Path in the OAuth2 User JSON to the username. eg: user.username'
     oauth2_json_name_path: "Path in the OAuth2 User JSON to the user's full: user.name.full"
     oauth2_json_email_path: "Path in the OAuth2 User JSON to the user's email: user.email.primary"
+    oauth2_json_avatar_path: "Path in the Oauth2 User JSON to the user's avatar: user.avatar_url"
     oauth2_email_verified: "Check this if the OAuth2 site has verified the email"
     oauth2_send_auth_header: "Send the token as an HTTP Authorization header"
     oauth2_debug_auth: "Include rich debugging information in your logs"
     oauth2_authorize_options: "When authorizing request these options"
+    oauth2_scope: "When authorizing request this scope"
+    oauth2_button_title: "The text for the OAuth2 button"
 

config/settings.yml

@@ -30,6 +30,7 @@ login:
   oauth2_authorize_options:
     default: 'scope'
     type: list
+  oauth2_scope: ''
   oauth2_button_title:
     default: 'with OAuth2'
     client: true

plugin.rb

@@ -40,6 +40,9 @@ class OAuth2BasicAuthenticator < ::Auth::OAuth2Authenticator
                         if SiteSetting.oauth2_send_auth_header?
                           opts[:token_params] = { headers: { 'Authorization' => basic_auth_header } }
                         end
+                        unless SiteSetting.oauth2_scope.blank?
+                          opts[:scope] = SiteSetting.oauth2_scope
+                        end
                       }
   end