Map section revealing added

UI changes:

- The reveal map section functionality finally added to the game, so now if the starting visibility is set to false the map section will not be visible, but the reveal button is displayed instead. You can only reveal 1 map section, then the buttons dissapear and will only apper again after the player survived a wave. The reveal buttons only appear next to already shown sections where path leads into them.

Gameplay updates:

- Pathfinding is now calculated every time a new map section is revealed, so only shown map sections are taken into account.

Bug fixes:

- Camera handling is now not affected by game speed changes.