Added support for configurable reserved usernames (fix of #1382) (#3566)

* Added support for configurable reserved usernames

* Added reserved usernames from mastodon issue 1355

* Fix reserved usernames

config/locales/en.yml

@@ -40,6 +40,7 @@ en:
     posts: Posts
     remote_follow: Remote follow
     unfollow: Unfollow
+    reserved_username: The username is reserved
   activitypub:
     activity:
       announce:

config/settings.yml

@@ -7,7 +7,7 @@
 # For more information, see docs/Running-Mastodon/Administration-guide.md
 #
 defaults: &defaults
-  site_title: 'Mastodon'
+  site_title: Mastodon
   site_description: ''
   site_extended_description: ''
   site_contact_username: ''
@@ -27,6 +27,13 @@ defaults: &defaults
   interactions:
     must_be_follower: false
     must_be_following: false
+  reserved_usernames:
+    - admin
+    - support
+    - help
+    - root
+    - webmaster
+    - administrator
 
 development:
   <<: *defaults