Fixed two cost handling bugs.
- Receiving the current cost multiplier from the TankContentSwitcher leads to an exception when the TankContentSwitcher has not been initialized yet.
- When recovering a vessel, the price of the procedural part would be handled as 0. Easy way to fix this: calculate costs only in editor and save it to persistence.
Merge pull request #79 from ItMustBeACamel/bug_costs

Fixed two cost handling bugs.