Improve replay metadata and the replay browser

List of changes:

* Better and more filters with new layout, for both mods.

* Rename/Delete/Detele all functionality.

* Simplified ReplayMetadata class considerably by introducing a new
GameInformation data object. The new GameInformation class contains
more information than previously available so the new solution is not
compatible with old replays, meaning it can't read old replays.

* Better and cleaner game information gathering in order to be written
at the end of the replay file.

* Revert changes to ReplayConnection, no longer necessary.

* Better exception message on missing sprites and fonts.

* New "SpawnOccupant" class that holds all the information needed by the
MapPreviewWidget to visualize a spawn point. It was using Session.Client
before and it was necessary to separate it to be able to show information
not available at lobby time.

* Fix keyboard focus UI bug when closing a window would not remove focus.

OpenRA.Game/Game.cs

@@ -263,10 +263,6 @@ namespace OpenRA
 			using (new PerfTimer("LoadComplete"))
 				orderManager.world.LoadComplete(worldRenderer);
 
-			var rc = orderManager.Connection as ReplayRecorderConnection;
-			if (rc != null)
-				rc.Metadata = new OpenRA.FileFormats.ReplayMetadata(DateTime.UtcNow, orderManager.LobbyInfo);
-
 			if (orderManager.GameStarted)
 				return;