WindowServer: Add support for cursor themes

Now you can specify a CursorTheme key in /etc/WindowServer.ini. The
cursors are loaded from /res/cursor-themes/<name> directory. This
directory contains a Config.ini file with format similar to previous
Cursor section, except it uses relative paths.

This commit adds also Default theme, which uses cursors being
previously in /res/cursors.

The WidgetGallery is updated to match the new cursor path format.

Base/res/cursor-themes/Default/Config.ini

@@ -0,0 +1,17 @@
+[Cursor]
+Hidden=hidden.png
+Arrow=arrow.x2y2.png
+ResizeH=resize-horizontal.png
+ResizeV=resize-vertical.png
+ResizeDTLBR=resize-diagonal-tlbr.png
+ResizeDBLTR=resize-diagonal-bltr.png
+ResizeColumn=resize-column.png
+ResizeRow=resize-row.png
+IBeam=i-beam.png
+Disallowed=disallowed.png
+Move=move.png
+Hand=hand.x8y4.png
+Help=help.x1y1.png
+Drag=drag.png
+Wait=wait.f14t100.png
+Crosshair=crosshair.png