Make django use_tz

Tell segment IO whenever a page is loaded.  Once this works, we
can add more detailed instrumentation for events we care about.

Will be turned off in prod until the SEGMENT_IO_LMS feature flag is
set to True and a SEGMENT_IO_LMS_KEY is set.

Allow themes to override contact and bugs email addresses via the
settings.

Configure the technical support email address in the settings so that
themes can override with an email of their own in the appropriate
env.json file in production.

This setting is used to control the display name of the platform. The
default is "edX", but themes may wish to override. For example,
Stanford will use "Stanford Online" for the time being.

The `FAVICON_PATH` setting determines the location of the favicon for
the site. It's automatically adjusted when a theme is enabled,
establishing the convention that themes will place their favicon in
`static/images/favicon.ico`.

Rather than directly invoke command-line Python (and Mako) from the
assets Rakefile, or call an external Python script, use a Django
management command to preprocess all asset template files.

An "asset template file" is defined as a static asset file with a
file extension indicating that it needs to be run through a template
engine prior to Sass/CoffeeScript compilation or packaging with other
assets. The preprocess_assets management command will look through
all of the files listed in the `STATICFILES_DIRS`, preprocessing each
as needed. Preprocessing strips off the special template file
extension, creating a new file in the process.

Currently, the only variable accessible in an asset template file is
the `THEME_NAME`, defined in the settings.

This commit adds the requisite settings and startup features to
enable integration of themes into the edX platform. It does not
yet provide hooks in any of the templates, but it does cause the
main `lms/static/sass/application.scss` file to `@import` a theme's
base Sass. Template hooks will come down the road.

CHANGELOG
---------
Define a new `MITX_FEATURE`, `USE_CUSTOM_THEME`, that when enabled,
can be used in templates to determine whether or not custom theme
templates should be used instead of the defaults.

Also define a new setting, `THEME_NAME`, which will be used to
locate theme-specific files. Establish the convention that themes
will be stored outside of the `REPO_ROOT`, inside the `ENV_ROOT`,
in a directory named `themes/`. `themes/<THEME_NAME>` will store
the files for a particular theme.

Provide a function, `enable_theme`, that modifies the template and
static asset load paths appropriately to include the theme's files.

Move the main LMS Sass file to a Mako template that conditionally
`@import`s the theme's base Sass file when a theme is enabled.

Add logic to the assets Rakefile to properly preprocess any Sass/
Mako templates before compiling them.

Start linting envs files, add task to only pylint errors, and move pylintrc file to the correct location

The MKTG_URLS dictionary is overwritten completely in aws.py anyway, and we
shouldn't be trying to keep both the production config and LMS code in sync
with changes to the marketing site.

* Fix indentation/line break issues
* Handle marketing root URL as a separate case in marketing_link
* Move link map to its own setting.

This functionality requires the Zendesk URL, user, and API key to be specified
in django.conf.settings. Also, add a flag to MITX_FEATURES (enabled by default)
to control the endpoint and the front-end feature (yet to be added).

This allows us to a) compile the coffeescript and sass from xmodules
using the new out-of-band method and b) reload xmodule static content
whenever it changes, which should make devs much happier.

When a user logs in this will drop a new cookie 'edxloggedin' that will
match the value and expire date of the django session cookie.
When a user logs out the cookie will be removed