Tooltip

Changed the skybox (actually there are three in the source tree right now.. maybe we can change them according to time of the day.. or province?)

Also implemented a tooltip that appears when you hover over a building icon to indicate the cost. In order for this to be realtime updated you need to to call 

   menu.setResourcesValue

When the server has updated the resources a player has. When a player has insufficient resources the text will appear red.