Add genre, composer, and performer tags and use them
Merge remote-tracking branch 'upstream/develop' into feature/extra_tags
Date is not mandatory AFAICT
Merge branch 'develop' of https://github.com/mopidy/mopidy into feature/extra_tags
Fix testcases after merging mopidy/develop
Added a ton of extra tests and expanded a few to include new tags
Add missing regexp
Add frontend MPD tests for 'search comment "foo"'
Add more tests
main: Move argparse building to a function.
main: Create helper for logging boostraping
main: Start unifying command handling

- Removes show_deps and show_config from commands module. These
  are now handled directly in the main() method pending subcommands.
- Unifies show_config with general main() config handling.
- Sets default verbosity level to zero.
- Reduce verbosity when --show-config or --show-deps is called.
- Update console logging to consider verbosity < 0 quiet/
main: Switch to subcommands

- show-deps replaced with 'mopidy deps'
- show-config replaced with 'mopidy config'
- Just running mopidy now displays help, run 'mopidy run' to start server.
main: Improve main bootstrapping sequence

- Parses args in two pases to allow for setup of logging well before doing
  extension sub-commands.
loggin: Add DelayedHandler to root logger.

The delayed handler:
- Accepts and buffers logs until they are released.
- Upon release the logs are re-posted to the root logger.
- After release log records are ignored.

This allows us to avoid the silly tricks we've been doing with parsing args and
config early for the sake of bootstraping logging. Now we can just start
logging and once the logging has been setup the messages are released and
handled according to the correct settings.
main: Move default subparsers into commands module

Also switches to using dest for storing the chosen sub-parser.
ext/backends: Add get_sub_commands and BaseSubCommandProvider
main: Wire in actual execution of sub-commands.
ext/backends: Add extensions to sub commands run
local: Add 'mopidy scan' command via extension sub-commands.