First pass at Gstreamer 1.0 porting.

This at least compiles against gstreamer 1.2.
Things that work:
* Playing audio
* Automatically completing tags

Things that don't work
* Spotify
* Moodbar

Things I haven't tested
* Transcoding
Merge branch 'master' into gstreamer-1.2
Fix slow library search on sqlite 3.8.

(cherry picked from commit 56dade25981da1656cbb68447e8518529e229978)

Conflicts:
	src/library/libraryquery.cpp
Add explanatory comment to last commit.

(cherry picked from commit 5fffbbc6898dc8373d6fd5bf28d4cd79d6f089d5)
Fix compiling 1.2 branch on GCC 4.9
Bump 1.2 release version
Bump changelog for 1.2.3

(cherry picked from commit 2e61ef9b178b20652590832b7d36038c73d0bbf5)
Add missing header for syscall().

This is cunningly not defined in syscall.h

(cherry picked from commit 3df3a5b645737603af6bda844db04c431b9c8064)
Add missing header for _exit()

Fixes #4188

(cherry picked from commit acfc7e6d2196f9ecb080b5405cd78066734bbc39)
Add missing include for symlink()

(cherry picked from commit 7671108aa8d02658cd35cacf4337507cc80ea03a)
Bump installed dependency DLL versions.

(cherry picked from commit 49c2fe8de11e06838feea34afa20aac4db187cbe)
Add new DLLs to windows install.

(cherry picked from commit 8c2f927bc22c32502d3a0673e9bc6c768543d31f)
Install libffi DLL.

(cherry picked from commit 1c3cee87192496b9439596ca50526bf14f760a95)
Add more things to the 1.2.3 changelog
(cherry picked from commit e8a0c1cd9f49943606e558331cd097ac888c9f70)
Add test for MusicBrainzClient.
Parse discid xml from MusicBrainz correctly. Fixes #4025.
Reset the model during init of CddaDevice

This ensures that the track list in the device tab is correctly updated when a
disc is replaced with one that doesn't exist in the MusicBrainz database.
Make mock_network_ a std::unique_ptr and create it in SetUp() instead of SetUpTestCase().
Add an AppData file.  Fixes #4381
Set a minimum height on the equaliser sliders.  Fixes #4380