Allow high resolution graphic replacements

[squiddingme]

Description

It should be possible to replace sprite atlasses with higher resolution versions. SpriteAtlasSerialization and the format of .atlas files suggests you can set the scale of the sprite sheet on the second line, but a quick test suggests this is very broken and wasn't fully implemented.

Notes
A tileset size.txt file exists in the Data/Maps/Tileset folder.

The contents of the file are as follows:

// this file can be used to set the size of tiles for tilesets that do not uses tiles that are 16x16
//dungeon five.png:32
//tileset0.png:48

This allows you to override the default tile size (of 16x16) for any given tileset, and actually works but is unused by the game. It may be worth splitting this off into per-tileset files (e.g, for tileset0.png, there is a corresponding tileset0.tileset file) instead of one global file with multiple entries.