[UI] Resource icons

[hooster1]

When you get time, the resource harvesting icons could use some updating.

Mines and quarries use the same symbols.
Farms and Hunting lodges us the same symbols.

All, including outposts could use an under construction symbol to let us see it is not available yet.

When construction is complete, please ask the user if he would like the workers and followers to return to the tower. Not sure if they help production, perhaps a little note showing the additional production being provided by the workers / followers would be good to add to the question about going home.