web: Remove WebSocket demo page
web: Make pages fill mobile viewports
web: Use font similar to mopidy.com
web: Remove focus on 'HTTP frontend'
web: Strip down CSS
http: Extract helper for setting common response headers
http: List installed web clients at /mopidy/
http: Test serving og legacy static_dir apps
http: Redirect from root to /mopidy/ if no static_dir app
http: Fix flake8 warnings
docs: Update changelog
Merge pull request #759 from jodal/feature/web-client-selector

Add web client selector