Texture config

[alex-irt]

Textures need details about the texture type, connected texture types and random spawn chance. Using the file name is quickly becoming unwieldy so a texture config is needed where all these things can be specified. In addition the texture index should split fetching textures, fetching these files and then building an atlas out of the textures+configs. This will allow extending of the texture config system. This system should have default settings to use if a texture doesn't have any specified.

[alex-irt]

Updated alpha1 with some example texture configs, it should now support multiple textures in one file, connected textures in the same folder as the other textures with the connected texture type defined in the config and weighted random textures. The alpha1 branch is still unstable though but it's getting there.