Static texture classes are now proper CustomManagers

[kvakvs]

• Texture classes are not static anymore
• On level loaded, all textures are loaded too
• On level unloaded, textures are freed

In debug build this creates visible delay. Should we show a progress indicator or some short-time notification to let the player know that we're loading?

[krzychu124]

I didn't notice any issue with regards to memory leaking, or hot-reloading. Everything works flawlessly.

[chameleon-tbn]

all seems to work flawless with this build, therefor i give it a go.