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/Widgets/LabelWidget.cs

@@ -56,7 +56,10 @@ namespace OpenRA.Widgets
 
 		public override void Draw()
 		{
-			SpriteFont font = Game.Renderer.Fonts[Font];
+			SpriteFont font;
+			if (!Game.Renderer.Fonts.TryGetValue(Font, out font))
+				throw new ArgumentException("Request font '{0}' was not found.".F(Font));
+
 			var text = GetText();
 			if (text == null)
 				return;