UI Updates: Remove Start Page, Featured and Tweets

This part is only the removal from web.config.
Squash this with next check-in.
UI Updates: Remove Start Page, Featured and Tweets

Oops, forgot to remove Twitter and Featured API endpoints from
web.config.

Squash this down.
UI Updates: Remove Start Page, Featured and Tweets

Cleanup: Removed old start page code and replaced with calls to new
overlay code instead. Removed test menu as no longer needed. Removed
featured API/code that runs on server-side for featured list. Removed
anything to do with Twitter/tweeting. Fixed a few minor bugs encountered
during cleanup.

This code is ready for testing as a potential release but should not be
pushed to production just yet until one color change is implemented via
LESS only in a later check-in. (Prospective colors for background of
overlays are under discussion.)

Please note the addition to and removals from web.config. (Not just app
keys.)