Add filters to the replay browser dialog

This closes issue #2152. The filters added are:

* Game type (singleplayer / multiplayer)
* Date
* Duration
* Outcome
* Player name

Other changes:

* Added a 'CollapseHiddenChildren' option to the ScrollPanelWidget to
make hidden children take up no space.
* Removed the extension (.rep) from the replay filenames in the
replay browser.

OpenRA.Game/Widgets/ScrollPanelWidget.cs

@@ -30,6 +30,7 @@ namespace OpenRA.Widgets
 		public ILayout Layout;
 		public int MinimumThumbSize = 10;
 		public ScrollPanelAlign Align = ScrollPanelAlign.Top;
+		public bool CollapseHiddenChildren = false;
 		protected float ListOffset = 0;
 		protected bool UpPressed = false;
 		protected bool DownPressed = false;