Comprehensive themes used to allow you to override JS within one of the
bundles created for Studio and LMS (specified in the common.py env
files). So for instance, the bundle that becomes lms-base-application.js
is defined like this:

base_application_js = [
    'js/src/utility.js',
    'js/src/logger.js',
    'js/user_dropdown_v1.js',
    'js/dialog_tab_controls.js',
    'js/src/string_utils.js',
    'js/form.ext.js',
    'js/src/ie_shim.js',
    'js/src/accessibility_tools.js',
    'js/toggle_login_modal.js',
    'js/src/lang_edx.js',
]

You could not add a custom file to this list in your theme, but if you
created a themes/mytheme/lms/static/js/dialog_tab_controls.js, then your
theme's version of that file would be wrapped into the bundle, which
would be created at {staticfiles}/mytheme/js/lms-base-application.js

It doesn't appear that this functionality has seen much use in practice,
and it adds minutes to the compile time for sites compiling multiple
themes, so this commit removes this capability. It is still possible to
create and invoke custom JavaScript that is theme specific, and will
compile out to {staticfiles}/mytheme/js -- it's just not possible to
override a file that becomes part of the standard Studio/LMS bundles.

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

This reverts commit a796b563.

Conflicts:
	lms/envs/common.py
	openedx/core/djangoapps/theming/models.py
	pavelib/assets.py
	pavelib/paver_tests/test_assets.py

ziafazal: improvements need for multi-tenancy
ziafazal: fixed broken tests
ziafazal: no need to add setting in test.py
ziafazal: added hostname validation
ziafazal: changes after feedback from mattdrayer
ziafazal: fixed branding and microsite broken tests
ziafazal: make STATICFILES_DIRS to list
ziafazal: added theme directory to mako lookup for tests
ziafazal: added more protection in test_util
saleem-latif: Enable SCSS Overrides for Comprehensive Theming
saleem-latif: Incoporate feedback changes, Correct test failures, add tests and enable theming for django templates
saleem-latif: Correct errors in python tests
mattdrayer: Fix invalid release reference
mattdrayer: Update django-wiki reference to latest release
saleem-latif: Update Theme storages to work with Caching, Pipeline and collectstatic
saleem-latif: Incorporate feedback changes
mattdrayer: Pylint violation fix
mattdrayer: Fix broken pavelib test

This reverts commit 954dae58.

ziafazal: improvements need for multi-tenancy
ziafazal: fixed broken tests
ziafazal: no need to add setting in test.py
ziafazal: added hostname validation
ziafazal: changes after feedback from mattdrayer
ziafazal: fixed branding and microsite broken tests
ziafazal: make STATICFILES_DIRS to list
ziafazal: added theme directory to mako lookup for tests
ziafazal: added more protection in test_util
saleem-latif: Enable SCSS Overrides for Comprehensive Theming
saleem-latif: Incoporate feedback changes, Correct test failures, add tests and enable theming for django templates
saleem-latif: Correct errors in python tests
mattdrayer: Fix invalid release reference
mattdrayer: Update django-wiki reference to latest release