When RTSP is shut down, the server destroys sessions (with no locking)
while clients are still able to concurrently access them, potentially
leading to a crash. Make sure we unregister the RTSP URL before
cleaning up (then indeed no locking is needed).

This is ugly, but I don't know how to do it the correct way.
The UI is not top-quality yet, but it works. Feel free to improve.

When an ES is removed, it is possible to set up a track that won't be
cleaned up and will remain dangling, causing a crash later. Make sure
we unregister the RTSP URL before cleaning up.

'one-instance' happens to work on Win32 though there are several issues:
- a WM_QUIT is sent to the helper thread when any instance terminates
 (the master or a secondary instance). 'one-instance' should then stop
 working as soon as the first secondary instance terminates.
- But, sending WM_QUIT via SendMessage directly calls the window
procedure callback. And this callback here doesn't process the message
at all. Therefore, it is a no-op and the thread is actually never stopped.

This patch does the following :
- move the WM_QUIT message to ensure that only the master (first) instance
 stops the helper thread.
- process the WM_QUIT message in the window procedure callback, and call
for clean termination of the thread.

Note that PostQuitMessage cannot be directly called as there are two
distincts threads here.

As far as I know, the distinction only matters anymore in the input
loop, for E/S out decoders (due to the evil ObjectKillChildren).

Remove moved files, they don't contain any translation

RTCP sockets of RTSP sessions are not closed when the input is stopped.

libvlc*.so are not yet configured, so we can't use the installed
vlc-cache-gen just yet.

If the same module (i.e. currently same file path) is scanned more than
once, the linked list would get corrupted, and VLC crash while loading.

This could happen, e.g. if you put $(vlclibdir) into --plugin-path.

Keep application default font family.
Make Title italic.
Make both Title and Artist bold only if it is the current item.

Also delay view creation in constructor after the title label has been created

This enables usage of vlc extension in Lunettes.

This needs to be splitted in a separate files.
VLCDialogGridView still suck, and won't place items as we would expect them.

It fixes zoom settings at the core level (partially close #3245).
"zoom" cannot be removed as it provides a list of choices while "scale" is
a free value. The names aren't great, but that can wait.