2. Update COMPREHNSIVE_THEME_DIR to COMPREHENSIVE_THEME_DIRS
3. Update paver commands to support multi theme dirs
4. Updating template loaders
5. Add ENABLE_COMPREHENSIVE_THEMING flag to enable or disable theming via settings
6. Update tests
7. Add backward compatibility for COMPREHEHNSIVE_THEME_DIR

The old code set the output-encoding to None, which means, I want
Unicode strings as output.  This made Mako pass markupsafe objects to
"unicode()", which applied all the escaping.  Then the result would be
given to Django, would would html-escape it again, resulting in
over-escaping.

By setting the output-encoding to utf8, we use filters.encode.utf8
instead, which is aware of Markupsafe, which avoids the over-escaping.

Mako filesystem/app_directories loaders already wrap default django template loaders.

Mako loaders delegate the `load_template_source` method to the base loader that
they wrap, so there's no reason to explicitly include the two django loaders in the settings.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

This makes these files importable, and puts them into the new best guess
as to where files should live.

When loading a Mako template from a Django template, the file
encoding of the Mako template was left unspecified. In some cases,
this would cause the Mako template to be interpreted as an ASCII
template, resulting in blowups if the template was encoded in
UTF-8 (e.g., lms/templates/footer.html).

Now, both the input and output encodings are specified as UTF-8.