More mechanics!

In this update we added the following:

* A sprint mechanic (shift)
* A dash mechanic (F-key)
Both can currently used to test which mechanic fits the game better.

* Steadily depleting health in the ice level
This mechanic spawned from the idea to add some sort of danger to the level. The idea: The cold weather is always dealing damage to the player, except if the player positions near a warm source (a campfire, for example).