Make windows resizable

If we were to make our own window background patterns, we could implement a simple mirrored tiling scheme for drawing the `View` background, then we could easily make windows resizable further eliminating the need for a widescreen mod. It wouldn't be very difficult for anybody inclined. I dont know if we have an appropriate cursor tho.

The originals had the control backgrounds integrated with the window background, but GemRB has the capability to display backgrounds on any `View` so we could just script our own backgrounds in for anything that we need one for.

Admittedly this would be a lot of artistic work to look good. Something far from my abilities.

The issue mentions the View background, mirrored tiling, resizable windows, cursors, and scripted control backgrounds, but names no files or tests. Start by locating the View implementation and the existing window-sizing and input handling entry points. Done would require a defined resizing approach plus the background and cursor treatment needed to make it usable.

Written by the indexing model from the issue text.