build: Rework build configuration for GStreamer backends

Using a PLAYBACK_BACKEND variable in SUBDIRS is incorrect, as it
always causes one of the backends to be omitted from the source tarball,
thus breaking "make distcheck".

The two GStreamer backends can now be built conditionnaly, with the
appropriate --enable-gst-sharp and/or --disable-gst-native configure
option.

By default, only the native backend is built, as was the case before.
You can choose to build both backends, or none if you want Banshee to be
very silent...

An indication whether the native backend will be built is added to the
configure output, for clarity.
hyena: Update to latest git master, to bring in fixes for unit tests
build: Don't run the unit tests during distcheck

We're not quite ready to run the unit tests as part of "make distcheck":

 * Some tests fail because they can't find the test data when being run
   from an out-of-tree build, like distcheck does.
 * Failures do not stop the distcheck process, so they quickly scroll
   away, making them hard to spot. And since it takes some time to get
   to the test, you're probably not watching your terminal for several
   minutes...
MediaPanel: Remove MediaPanelTheme

The specific visual adjustments in MediaPanelTheme were there to make
Banshee fit with the MeeGo UI, and also impacted the main UI.

As the MediaPanel is now a general purpose UI client, it should fit the
current theme, so we don't need those adjustments.
build: Use notify-sharp-3.0 when present on the system

Now that notify-sharp has a 3.0 release that depends on GTK 3, we can
use it and revert back to the same behavior we had in the GTK 2 world:
use the appropriate system-installed notify-sharp if present, and if
not, use our own internal copy.

This removes the --with-system-notify-sharp configure option, which
nobody should have been using anyway.
Let MonoDevelop 4.0 re-arrange the .sln and .csproj files

This is just the result of opening the solution properties without
changing anything, to let MonoDevelop 4.0 re-arrange the .sln and
.csproj files as it wants. This should prevent noise in later commits
that contain real changes.
Switch csproj files to Mono/.NET 4.0 target framework

This also upgrades the solution file to the Visual Studio 2010 format,
and updates Hyena to the latest git master, that now also targets the
4.0 framework.

This only impacts the build when using xbuild or building from the IDE.
The usual 'make' build is not affected.
Banshee.sln: Adjust naming convention policy to match our guidelines

Only real adjustment is to have lower case parameter names, the rest is
default values as set by MonoDevelop. Further refinements might be
needed to match our guidelines as described in the HACKING file, which
is still the reference.
build: Fix various issues when building with xbuild

Add some missing assembly references, in particular gio-sharp.

There are some issues left, but they seem mostly limited to projects
with platform-specific dependencies: OSX and Ubuntu-specific extensions.

Also update Hyena to the latest git master, to bring in some fixes in
its csproj files.
Use methods from cairo and pango bindings instead of the ones from Hyena

Update Hyena to the latest git master, which removes various custom
interop methods. Do the necessary adjustments to use the
corresponding methods provided directly by the cairo and pango bindings.
SqlDebugConsole: Fix build with GTK3
build: pkgconfig .pc to point to gtk3

The pkgconfig files that banshee generates for its
own assemblies where still being linked to GTK2. This
allows GTK3-compatible Banshee-Community-Extensions
to build properly with the new version of the toolkit.

Signed-off-by: Andrés G. Aragoneses <knocte@gmail.com>
TrackEditor: dispose local variable in a finally block

All Dispose() calls should happen in finally blocks to avoid leaks
when exceptions happen, so we apply a using{} block here.

Signed-off-by: Andrés G. Aragoneses <knocte@gmail.com>
Update Chinese simplified translation
Updated Czech translation
build: default to build just one media backend

Unless explicitly required by the user at configure time, the build
should default to only enable one media backend, not two at the same
time.

Banshee can run with more than one media backend, but this feature is
mainly intended for the use case of having two backends with different
capabilities. However, in this case we're talking about selecting the
managed or the unmanaged backend, and both (should) have the same
capabilities.

Before this patch, the user had to explicitly enable the managed
backend and disable the native one if she wanted to run the managed
one without loading the native one. This is now corrected: if the
user doesn't supply any option, only the native backend is built,
and if the user supplies the --enable-gst-sharp option, only the
managed one is built.
GStreamerSharp: update to work with new 0.99.0 version

The new 0.99.0 version of this binding targets GStreamer 1.0. This
has been an accomplishment that took many weeks, starting from the
Gnome .NET 2013 Hackfest in Vienna.

Contributions from:
 Stephan Sundermann,
 Olivier Dufour,
 Andres G. Aragoneses