#936 Introduce and use 'Termination' interface + improve termination request checking performance

• Best to review per commit.
• Non-end user visible changes:
  • Introduced Termination interface.
  • Use it in all projects, one by one.
• End user visible changes:
  • In Application classes, pass () -> isTerminationRequested() as lambda, not () -> AppEnv.isTerminationRequested(). The former uses the already known application environment, while the latter queries it for the thread. Saves a thread-local storage lookup, per termination check, thus improving the performance of termination checks. Applies to CIF to UPPAAL, CIF to Supremica, CIF code generator, CIF multilevel synthesis (not yet end user application), CIF explorer, CIF to PLC, CIF PLCgen, CIF controller properties checker, CIF data-based synthesis.

Closes #936 (closed)