A small UI update

I've re-designed the Unit Dispatch window to make it a bit more usable - it will now be permanently glued to the left side of the screen, like most of the other UI elements I've been adding recently.

This gives me much more screen space for displaying more units at a time, which should reduce scrolling. I'm now also grouping the available units by type, and sorting them in a repeatable and more understandable way. Previously, the units could show up in this window pretty much in any order they wanted to, making it impossible to find what you wanted quickly.

In the next update I will also introduce permanent assignments for passengers in the cars - the cars will remember who their last assigned driver was, and will let you skip finding a new driver each time you want to dispatch the car back to the map.