This PR adds additional partials to the default skeleton so that the styles get applied uniformly on bootstrap and non-bootstrap pages and also the discussion pages.
*Sandbox URL*: TBD - sandbox is being provisioned.
*Merge deadline*: None
1. Deploy an instance with the `simple_theme` role enabled and configured. Verify that SASS variables overrides and custom styles work.
[ ] @giovannicimolin
[ ] edX reviewer[s] TBD
Configuration Pull Request
Make sure that the following steps are done before merging:
[ ] A DevOps team member has approved the PR if it is code shared across multiple services and you don't own all of the services.
[ ] Are you adding any new default values that need to be overridden when this change goes live? If so:
[ ] Update the appropriate internal repo (be sure to update for all our environments)
[ ] If you are updating a secure value rather than an internal one, file a DEVOPS ticket with details.
[ ] Add an entry to the CHANGELOG.
[ ] If you are making a complicated change, have you performed the proper testing specified on the [Ops Ansible Testing Checklist](https://openedx.atlassian.net/wiki/display/EdxOps/Ops+Ansible+Testing+Checklist)? Adding a new variable does not require the full list (although testing on a sandbox is a great idea to ensure it links with your downstream code changes).
[ ] Think about how this change will affect Open edX operators. Have you updated the wiki page for the next Open edX release?