Set initial mixer volume for all mixers
Added mixer_volume to config documentation
Removed empty line (caught by flake8)
Forgot to adapt tests for audio actor
stream: Move mopidy.{backends => }.stream
local: Move mopidy.{backends => }.local
tests: Move mopidy.backends.dummy to tests.dummy_backend
backend: Remove unused BaseLibraryUpdateProvider
docs: Remove reference to dummy backend
Merge pull request #636 from jodal/feature/move-backends

Move backends out of mopidy.backends
backend: Move backend API to mopidy.backend

Keep imports from old locations working until extensions have been updated to
use the new location.
backend: Update backend API imports
docs: Update backend import
Merge pull request #637 from jodal/feature/move-backend-api

Move backend API to mopidy.backend
docs: Add mopidy.local.Library docs
docs: Actually include the Library class
docs: Fix param rendering
docs: Point Raspi users to the config and run sections

Ref. user not configuring or trying to run Mopidy at
http://www.raspberrypi.org/phpBB3/viewtopic.php?t=66074&p=484932
docs: Make extensions and clients more prominent on the front page
docs: More prose and less headers in ext docs