Rellocate template files to allow customizations.

Template paths of django apps should respect templates's namespace to be easy to customize in projects that includes the app. Check [notes of the template namespace][1] and [example of the files structure of django apps][2] for further reading.

  [1]: https://docs.djangoproject.com/en/1.6/intro/tutorial03/#write-views-that-actually-do-something
  [2]: https://docs.djangoproject.com/en/1.6/intro/reusable-apps/#your-project-and-your-reusable-app

**Changes in this commit:**
* Created `templates/django_bootstrap_calendar`  directory and moved templates files to it (only `base.html` was not moved since it shouldn't be part of the app).
* Updated references to the templates, even in comments like `.po` language files.