Collision boundary view for Practice Mode

Added an option to show the collision boundaries of the game in Practice Mode. I decided to add this as it is not always clear where the collision boundaries are in the game and what can you actually collide against. Doing a complete graphics overhaul would be too time-consuming, but I think this is a great way to learn where the actual collision boundaries are in some confusing places.

Map changes:

• Decreased the chase time of one of the birds in the final section that could often land on the ice exactly on your way. It can still reach the ice but should always be passable from below.

Bug fixes:

• Fixed a couple of blocker obstacles under the bridges of part 6. It was possible to skate under some of the bridges that were supposed to be blocked.

• Fixed a bug where in the Permafall mode the timer showed double the time once you fell.