Loader loads textures dynamically

meta.txt:
- added a txt file with meta information about textures (id, path,
renderlayer and frame dimensions)

CTexture:
- fixed a memory leak: now properly destroys the old SDL_Texture upon
reloading

CLoader:
- complete rewrite of CLoader
- now uses a map to store CTexture id's and the required constructor
parameters
- id's and constructor parameters are loaded in CLoader construktor from
a file
- Loader can be requested to create texture objects for a specific or
all id's
- getTexture(string id) to retrieve the corresponding CTexture instance
if avilable
TODO:
- move splitstr from CLoader constructor to separate function
- unload CTextures

BUGS:
- some tiles (~ 1/4th) flicker when player moves, other sprites seem to
be fine.