Save / Continue simulation

[Ozaq]

We want to allow saving and restoring simulation state so that users can pause and resume a simulation at a later point in time.

Constraints:

• The implementation shall provide for a mechanism to store arbitrary model data (support for future models)
• Whatever is saved to disk shall NOT be part of a public interface, no guarantees will be made about stability
• No compatibility guarantees shall be provided in this implementation, i.e. You will only be able to resume a simulation with the exact version it was saved from.