#269 Allow converting more/extra updates/predicates/expressions.

• Small changes needed for our research.
• Made a few methods public in the conversion class, to allow converting more updates/predicates/expressions/etc after the regular conversion.
• Needed to make a few methods static as well, to allow invoking them outside/after the regular conversion.
• The problems become parameters then. This should change to a proper precondition checker using our new checker framework later on, but that is out-of-scope here.

Addresses #269