Visual Overhaul (and More Levels and Bug-Fixes)

As said in the caption there are visual improvements. One consists of removing a lot of text and replacing it with icons.

Some playtesters complained about to much text and with the icons "tutorial-levels" feel much less like a tutorial.

Then I increased the number of used textures and switch between different texture-sets throughout the levels.

I certainly will need to come back to the visuals at some point and make further adjustments/additions, but for now I'm actually quite satisfied how the increased variety improves the overall appearance.

Furthermore, there are two new levels.

One level elaborates on the difference in movement behavior between <-> arrows and -> arrows, since playtests emphasized that this might be necessary.

The other new level builds on the idea of progressing via moving frames instead of the character movement.

There actually is already a similar level. However, since it appeared to be difficult for playtesters to grasp the concept I think it's a good idea to introduce the idea more carefully.

And of course there are also the obligatory bug-fixes:

• I found a very specific setup where certain collision weren't disabled correctly, giving the impression of collision with invisible walls. This necessitated a rework of the proximity calculation for box-shaped objects.
• Sometimes color could not be removed from objects without an obvious reason. This should no longer be the case.
• Due to incorrect update of some joints immovable objects could actually be slightly moved. This is no longer possible.
• etc.