Added namespace_id to project creation via API

This allows you to set the namespace ID for projects via the the API. By default it is created for the current user. You can assign it to the global namespace by passing `GLN` which translates to 'Global Namespace'.

lib/api/projects.rb

@@ -42,7 +42,8 @@ module Gitlab
                                     :issues_enabled,
                                     :wall_enabled,
                                     :merge_requests_enabled,
-                                    :wiki_enabled]
+                                    :wiki_enabled
+                                    :namespace_id]
         @project = ::Projects::CreateContext.new(current_user, attrs).execute
         if @project.saved?
           present @project, with: Entities::Project