main: Return status code 1 if {Backend,Frontend,Mixer}Error is raised
config: Support passing directories to mopidy --config
docs: Return exit status 1 on initialization error
config: Only load .conf-files when loading directories
docs: Add directories to --config in man page
docs: Fix grammar
Merge branch 'trygveaa/feature/mopidy-config-dirs' into release/v0.19.x

Conflicts:
	docs/changelog.rst
Merge branch 'release/v0.19.x' into develop

Conflicts:
	mopidy/config/__init__.py