Issue description was ambiguous.

Rephrased to be more precise.
Fixed typechecking. Apparantly it only happened with boolean selectboxes.
Removed not open for extension codesmell.
Fixed a bug in PHP boolean type evaluation
I'm starting to get the hang of this parentheses stuff.
Implemented all exprs
Parentheses are now only printed when they are needed.
Todo: Cleanup mess of parentheses.
Incorporate generic priority 'library' from Oberon0

It can be found here:
https://github.com/cwi-swat/oberon0/blob/master/src/ldta/oberon0/util/Priorities.rsc
Refactoring of parentheses complete.
Updated output README
Added compiler for checkboxes
Removed specialized selectValidator as it was not needed
Improved checkbox insertion
Getters and setters for HTML items from JS.
JS code now uses {get,set}FormValue
Merge branch 'kemi' of github.com:software-engineering-amsterdam/sea-of-ql into kemi
Using typemap to retrieve questions in QLS compiler
Merge branch 'kemi' of github.com:software-engineering-amsterdam/sea-of-ql into kemi
Extracted commonalities from grammar