Maintaining altitude

Several minor changes:

• In fly mode, the camera now maintains altitude instead of moving in the view plane
• New maps are created as being modified, and so are temp saved for play testing
• Each view now stores the camera orientation per map and transfers it when split
• Blockmaps and sets can once again be deleted, which broke in the recent overhaul
• It is now possible to pick the active layer using the number keys
• After loading a project, focus is set to the resource browser