Import sources: show only enabled sources

app/controllers/application_controller.rb

app/controllers/import/gitorious_controller.rb

app/controllers/import/google_code_controller.rb

app/views/projects/_bitbucket_import_modal.html.haml

app/views/projects/_github_import_modal.html.haml

app/views/projects/_gitlab_import_modal.html.haml

app/views/projects/new.html.haml

features/dashboard/new_project.feature

features/steps/dashboard/new_project.rb