Parser for the new sprite format

[heinezen]

Resolves https://github.com/SFTtech/openage/issues/1055

• [x] Introduce new .texture format for texture and subtexture definition
  • [x] specification
  • [x] converter export
• [x] Parsers for definition files
  • [x] sprite
  • [x] texture
• [x] Storage classes for animation data
• [x] Renderer test
  • [x] parsing
  • [x] displaying loaded texture

[heinezen]

[TheJJ]

merged as part of #1497