Added basic UI width slider and persistence
Optimisation WIP: Add classes to generate a texture atlas

New SCMAP.Knapsack, SCMAP.SystemLabel and SCMAP.TextureManager classes
which help building a texture atlas. As GPU memory use for distinct
label textures with a lot of whitespace is quite high, this should
optimise things greatly once implemented.
Label Sprite Atlas implemented fully

Sprite code moved out to SpriteLabel class as well. VRAM use is still
too high though, and still need to implement code to only redraw when
needed, and size down the label if it doesn't fit the texture.