Fix/issues

[francescofuggitti]

Fixes

fix 4 bugs:

• printing the type in actions parameters (issue Type print missing #36)
• parsing of And formulas in the effect of conditional effects (issue Conditional effects parsing #37)
• parsing of domain constants in pddl problems (issue Printing issue for constants in problem file #39)
• printing predicates and objects types (issue problem_to_string does not work correctly #28)

Types of changes

What types of changes does your code introduce?
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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• I have read the CONTRIBUTING doc
• I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...