Implement MSAA

[qzed]

Implement Multi-Sample Anti Aliasing. This requires changes in:

• The default frame-buffer to allow MSAA for overlays,
• PreRenderedTileProvider to allow MSAA for pre-rendered tiles,
• TileBasedVisualizer to allow MSAA for non-pre-rendered tiles (this is superfluous when used with anti-aliased pre-rendered tiles, so this would be more of a nice-to-have feature).

[dominicparga]

MSAA can be changed in video games' graphic options. We could add such options to the preferences in the main-ui.