Relocate filters, move texture render, fix mouse coords

* The whole filter pack was relocated from
jangoDare.graphics.postProcessing to jangoDare.graphics.filters - this
makes a lot more sense, because filters can also be applied to textures
for example and are not only used in post-processing any more.
* While I'm already relocating things, I also had to remove
Display.renderTexture() and make Texture.render() the active part. This
better follows the extensible and modular structure I try to achieve
with this engine.
* A bug was fixed where display scales with decimal places would result
in wrong mouse coordinates, due to unnecessary casting to int.

Unfortunately, this commit will break a lot of code. At least it broke a
lot of mine.