Revert "Remove 'mad' from 'mopidy deps' listing"

This reverts commit cb6e19c039d2a49be235a34dcf05236b3f24625a.

The "mad" element is the only way to decode MP3 with GStreamer 0.10 on OS X.
deps: Add flump3dec (and mpg123audiodec) to Gst element list
deps: Remove GStreamer mixers from element list
http: Allow WebSocket requests from other hosts

This makes Tornado 4.0 behavior consistent with previous Tornado versions.

Fixes #788
audio: Set initial volume on software mixer

This must be set after the audio actor has injected itself into the software
mixer, else it will have no effect on the GStreamer software mixer.

Fixes #791
docs: Improve readme

Use text from www.mopidy.com. Change "Download development snapshot" link,
which confused some new users.
Remember about upgrade changes and sourcing bashrc
Merge 'ifosch/patch-1' into develop
docs: Tweak OS X path changes
docs: Update authors
version help test fixed
Merge pull request #793 from ifosch/help-version-test-fixing

Help message test doesn't complain now when using external PYTHONPATH
mpd: Fix crash on wrong number of command args

Fixes #789
docs: Update changelog
docs: Update changelog
Bump version to 0.19.2
Release v0.19.2