GitLab

* texturemanager documentation and parameter fix
* imagerepresetation conversion fix for channel number mismatch

TextureManager now uses a configurable lifetime for the lifetime of a cache object. Upon every garbage collection event, the counter is incremented for each object in the cache and if a counter exceeds TextureManager::garbageLifetime, the texture id is marked for deletion.
Deletion now happens in a separate thread, as a job enqueued to the OpenGLJobProcessor, in order to properly acquire a valid opengl context.

Now spawns a garbage collection thread that periodically clears the cache. Still not optimal but at least gets rid of unused memory at some point. For next iteration, a "smart" garbage collection (time- or query based heuristic)

* Updated TextureManager
* Fixed some warnings and minor cleanup

Texture manager manages textures in a cache, for more efficient texture reuse. Currently only clears the cache on program exit, no garbage collection, disabled by default.