Adds firefighter and police starting scenarios.

What's so special about these as opposed to starting in the evac shelter
as a firefighter or cop? If you choose one of these you start in a fire
or police station full of zombies, but the cost of your choice of
profession is reduced via an intrinsic property of the scenario system
so there's a bit of incentive points-wise to start in a
less-advantageous environment specific to that profession for a more
appropriate (and difficult) origin scenario.

tl;dr - Get cheaper professions in exchange for a more Fun start.