Added ability to copy a page

In 'More' menu alongside move.
Allows you to move if you have permission to create within the new
target parent.
Closes #673

resources/lang/en/common.php

@@ -31,6 +31,7 @@ return [
     'edit' => 'Edit',
     'sort' => 'Sort',
     'move' => 'Move',
+    'copy' => 'Copy',
     'reply' => 'Reply',
     'delete' => 'Delete',
     'search' => 'Search',