Rellocate template files to allow customizations.

* Move templates to the dir django_bootstrap_calendar (only base.html was not moved since it should not be part of the app).
* Update references to the templates.
Modernized and optimized serializer function.

* Changed deprecated django.utils.simplejson to json.
* Removed parameter "encoding='utf-8'" in the json's dumps function call.
* Improved creation of the dictionary local variable objects_head in function event_serializer.
* Improved docstring of the serialization function.
* Created file test.py with a TestCase for test serialization of an event.