Modernize UIExamples

Summary:

• Get rid of an AphrontSideNavView callsite.
• Modernize and simplify the application implementation.
• Doesn't work perfectly on tablet/phone but that's because not all the UI examples work there yet.

Test Plan: Looked at /applications/ and /uiexample/.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3431