Estimate current income rate

In order to fix #37, we need to be able to accurately estimate our immediate income rate, future income rate, and predict how long it will be before we can afford future build order items (while training military units/tech). This also affects other issues related to macro economy planning, resource mix (mineral/gas ratio), and expansion timings.

Use as example:
https://github.com/BurnySc2/sc2-planner/blob/master/src/game_logic/income.ts