Cover ApplicationController#authenticate! in specs.
Add bundler caching for travis.
Use container in travis.
Add shoulda-matchers gem.
Remove todo.
Rewrite User#find_or_create_with_omniauth spec.
Add todo.
Make sure the user OAuth UID is unique.
Move the initial user place import in a callback.
Add documentation for User#initial_places_import.
Rename User#find_or_create_with_omniauth to User#from_omniauth.
Rename User#create_with_omniauth to User#create_from_omniauth
Fix typo.
Add possibility of having several authorized uids.
Create a PlaceImporter model.
Make sure default are set in the PlaceImporter.
Better doc for PlaceImportJob#perform.
Add PlaceImporter#first_import?.

Before, I planed to have a default value in for the `last_imported_at`
field. However, the first and initial import shouldn't have this field
set since this is how we actually know whether it is the first import.
Simplify Place model.
Extract foursquare client in private method.