StreamPositionLabel: Fix rendering of the label and the progress bar

Render the label in the right position, and use the appropriate classes
to have a good-looking progress bar.

It is only now that I was able to understand the original trickery in
drawing that widget. If the progress bar is visible, we first draw the
part of the text that is over the progress bar, to have it in the right
color.
ConnectedSeekSlider: Make the stream position label visible again
SeekDialog: Make the stream position label visible again
DiscUsageDisplay: Remove useless transform & clip

Signed-off-by: Bertrand Lorentz <bertrand.lorentz@gmail.com>
DapPropertiesDisplay: Fix coordinates for rendering the frame

Signed-off-by: Bertrand Lorentz <bertrand.lorentz@gmail.com>
Port the custom gtkrc handling to the new CSS-based theming

The customization is now done by putting CSS statements in a gtk.css
file. This file must be loaded after GTK is initialized, because we need
the default GDK screen.

Rename the two related command-line option to no-gtkcss and
debug-gtkcss, and add a description for debug-gtkcss.
GtkElementsService: Port the gtk-menu-popup-delay hack to Gtk.Settings

I'm not sure the bug still exist, but there is no drawback in playing it
safe, just in case.
DateButton: Re-format the code, no real code change
DateButton: Port the grabbing code to the new Gdk.Device API
Replace the last occurrences of SizeRequest with GetPreferred* calls
SoundMenu: Remove optional dependency on indicate-sharp

Indicate-sharp was only useful on Ubuntu 10.10 to register with the
sound menu. It is not needed in more recent versions, so we can drop it.
SoundMenu: Fix build with internal notify-sharp

In order to build with our internal notify-sharp, the SoundMenu
extension needs a reference to the NotificationArea assembly that
contains it.
AppleDeviceSource: Fix build error caused by mixing glib-sharp 2 and 3

As libgpod-sharp brings in glib-sharp-2.0, this causes a compiler error
when referencing anything from the GLib namespace.

Be aware that this only fixes the compile-time problem, bad things are
probably going to happen at runtime as long as libgpod-sharp is not
ported to glib-sharp 3.0.
i18n: Update POTFILES.in
Added initial skeleton of uPnP Client addin
Added initial referencing to needed dll's in Mono.Upnp, this should probably be done via configure somehow
Made UPnPClient add only real MediaServers as sources
Added the missed translation file
Give the source both the uPnP device and the contentDirectory (if found)
Add found music tracks in content directory to UPnPSource