Merge branch 'master' of github.com:stonaz/nodeshot into refactoring

Conflicts:
	nodeshot/core/layers/serializers.py
tinyMCE editor fixed
Interoperability: NodeExternal model is a cleaner solution to store external layers info
CitySDK mixin provides methods to syncrhonize the local DB with an external CitySDK API (WP5)
OpenWISPCitySDK synchronizer
ProvinciaWIFICitySDK synchronizer + cleanup
minor fix to CitySDKMixin
run synchronizing tasks in the background with celery
customizable status model draft
fix HTML editor on mailing.outward
configurable status completed
interoperability cleanup
OpenWifiMap interoperability draft
UI moved to interface app