Merge branch 'fix/import-sources' into 'master'

Add missing import source

I realised https://gitlab.com/projects/new is missing the `gitlab export` option, while this worked fine in GDK it seems that something was missing here.

This _should_ fix it unless I'm missing any other `import_sources` (did a grep and couldn't find it anywhere else though).

See merge request !4825

config/initializers/1_settings.rb

@@ -215,7 +215,7 @@ Settings.gitlab.default_projects_features['container_registry'] = true if Settin
 Settings.gitlab.default_projects_features['visibility_level']   = Settings.send(:verify_constant, Gitlab::VisibilityLevel, Settings.gitlab.default_projects_features['visibility_level'], Gitlab::VisibilityLevel::PRIVATE)
 Settings.gitlab['repository_downloads_path'] = File.join(Settings.shared['path'], 'cache/archive') if Settings.gitlab['repository_downloads_path'].nil?
 Settings.gitlab['restricted_signup_domains'] ||= []
-Settings.gitlab['import_sources'] ||= ['github','bitbucket','gitlab','gitorious','google_code','fogbugz','git']
+Settings.gitlab['import_sources'] ||= %w[github bitbucket gitlab gitorious google_code fogbugz git gitlab_project]
 Settings.gitlab['trusted_proxies'] ||= []