Finished the rebalance and added costs.

Fixes #30 and #24.
Improved the InstallChecker

- Moved to run instantly instead of waiting for the main menu.
- Checks for changes done since 0.9.1.
- Added more logging.
- Changed the wording on the error messages shown to the user.
Fixed #36: added UI locks to prevent click-through

For both the Space Center and Editor scenes.