Implement support for repeated dives: save/open tissue state

[eianlei]

Now the planner does not support repeated dives where there is tissue loading from a previous dive.
To support repeated dives there must be:

• save to file the tissue compartment state at end of dive profile, JSON format would be easy & nice
• option to open for a new dive plan the previous state and configure the surface interval
• calculate a starting state from previous dive loading with surface time effect

At the same go could save the entire plan/profile with gases etc, and be able to read such saved files for later reuse