fix(datepicker): works without ng-model

This was one of the things we needed to fix on datepicker for the next version. It just needed a guard to check that there is a ngModel present.

For the tests, well, that is a hard part. There is no difference visually on the datepicker without ng-model, the only difference now is that it doesn't throw an exception :P. So I decided to test that the actual month is showed.

Testing for actual date is pretty hard because you can't hardcode anything so I decided to check that the title is the correct one.

I had to improvise a little bit on the year one :P

Ping @bekos