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
audio: Fix pep8 warning
Bump version number to 0.19
Merge pull request #759 from jodal/feature/web-client-selector

Add web client selector
docs: Update name/description of Mopidy MusicBox Webclient
js: Release v0.4.0
mpd: Create unique names for all items in browse

Replace the playlist uri/name mapping with a mapping for all the items
in browse. Check the mapping when browsing a path.

This has the added benefit of serving as a cache for browse, so we don't
need to traverse the path parts and lookup each of them for each call to
browse.
http: Fix missing placeholder in log statement

Related to martijnboland/moped#5
Add Mopidy-Spotify-Tunigo to list of extensions
Merge pull request #764 from trygveaa/docs/add-extension-mopidy-spotify-tunigo

Add Mopidy-Spotify-Tunigo to list of extensions