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
main: Ensure that exit_status_code always is assigned

KeyboardInterrupts are not always catched in commands.py. As far as I
have seen, if I/O operations are ongoing, a KeyboardInterrupt may be
raised there instead of in commands.py. In some cases, this may cause
loop.run() to return, which previously resulted in exit_status_code
being referenced before assignment.
network: disable_recv before telling actor to close connection

As of d62ad96, when the connection can't receive more data from the
client, it tells the actor to stop the connection and calls
disable_recv(). The actor operates in it's own thread and when it stops
the connection, disable_recv is being called again from a different
thread. Since the actor is told to stop the connection before
disable_recv is called, the two calls to disable_recv may happen
simultaneously.

This causes a race condition issue where both threads can reach past the
check that recv_id is not None before either of them set it to None. If
one of them set it to None before the other one tries to use it, an
error is raised.

This commit calls disable_recv before telling the actor to stop the
connection. Since disable_recv is a blocking call, this ensures that
recv_id is being set to None before the actor thread begins to stop the
connection.

Fixes #781
#818 Remove mopidy lux from documentation

(cherry picked from commit 06d7d650f870dfe55e02bc091f6f344df2762ef9)
tests: Test call order in test_recv_callback_gets_no_data
Merge branch 'release/v0.19.x' into develop
main: Log uncaught exceptions
main: Log uncaught exceptions

(cherry picked from commit 027b7a53fe9212853062da352c464c4277ade510)
mpd: Replace / with | instead of whitespace in playlist names
#818 Remove mopidy lux from documentation

(cherry picked from commit 06d7d650f870dfe55e02bc091f6f344df2762ef9)
(cherry picked from commit c230a0f64cf48eac18d72dc04827afe88220bcc6)
docs: Include mixers in concepts
docs: Unbreak API autodocs
docs: Add sponsors page