Add Bitbucket importer.

CHANGELOG

Gemfile

Gemfile.lock

app/assets/images/authbuttons/bitbucket_32.png

app/assets/images/authbuttons/bitbucket_64.png

app/controllers/import/bitbucket_controller.rb

app/helpers/oauth_helper.rb

app/helpers/projects_helper.rb

app/models/project.rb

app/models/user.rb

app/views/import/base/create.js.haml

app/views/import/bitbucket/status.html.haml

app/views/import/github/status.html.haml

app/views/import/gitlab/status.html.haml

app/views/projects/_bitbucket_import_modal.html.haml

app/views/projects/new.html.haml

app/workers/repository_import_worker.rb

config/gitlab.yml.example

config/routes.rb

...17123345_add_bitbucket_access_token_and_secret_to_user.rb