Display serverlist flags as icons

Marking this as WIP because I expect people will debate how the icons should look like. The code itself should work fine, though.

Screenshot:
![2014-12-01-005957_800x600_scrot](https://cloud.githubusercontent.com/assets/630411/5239964/e7b86a32-78f5-11e4-805f-f91bc0823cce.png)

I think it doesn't look different enough from three dots that warrants the risk of it being missing from the font.