#917 CIF controller properties checker: common check base classes and less duplicate check code

• This is another step for the issue. Not the last step.
• Changes are not end-user visible:
  • Introduced base classes for checks.
  • Renamed check classes.
  • Checker has list of checks and check them as well as report their conclusions through the API. Reduces code duplication.
  • Renamed MddPrepareChecks to CifMddSpec.
• Probably easiest to understand per commit.
• Probably best to review only the end result, since I took small steps and some things do change again in some later commits.

Addresses #917 (closed)