Added Toolbar / per save enabling. Contracts

- Added toolbar button to Space Center using new KSP toolbar API (from
0.24.0)
- Per game enabling/disabling of mod
- Resource rate / day now respects Kerbin / Earth day settings.
- Added Contract System framework
- First Pass resource audit.
- Tentative: All CO2 amount/maxAmount = 2 * crew capacity
  regardless of O2 amount/maxAmount. CO2 buildup is DEADLY.
- Default cabin air = 20x crew capacity. (has already been in effect
for awhile)