local: Use new config system
stream: Use new config system
lastfm: Use new config system
mpris: Use new config system
http: Use new config system
mpd: Use new config system
config: Add a Path config value and an ExpandedPath wrapper.

Allows us to easily use expanded paths, without losing the original value for
display and storage. In theory we could be using same trick for passwords.
config: Switch all paths and files to use the Path in schemas.

Also renames static_dir to static_path for better consistency.
Merge branch 'develop' into feature/use-new-config

Conflicts:
	mopidy/frontends/scrobbler/actor.py
mpd: playlist name disambiguation
mpd: Fix two test failures
audio: Use new config system
main: Use new config system
settings: Remove SettingsProxy at mopidy.settings
settings: Remove settings module
settings: Remove settings utils
mpd: fix style issues and type errors introduced in 87ce309
Tests are now OK
scanner: Use new config
config: Add path config value tests
Merge branch 'develop' into feature/config-path

Conflicts:
	mopidy/backends/spotify/__init__.py