Fixed tutorial02: Customizing project’s templates.

User should not put templates in ``mysite/mytemplates/``. Instead,
templates should be in ``mysite/templates/`` which is a convention.

Otherwise, if we wanted to keep ``mysite/mytemplates/`` then the
staticfiles tutorial should use ``mysite/mystatic/`` and that would just
be confusing.

Other djangonauts sitting next to me at Utrecht sprint (also working on
staticfiles documentation revamp) were also in favor of this change.

Also, the docs now demonstrate the setting with a Python list instead of a
Python tuple, removing the special note about the trailing comma. The
rationnale for this is that it is out of the scope of this tutorial to learn
Python tuple usage.