Semantic Analyser: PrintNode has not been verified

* Also traverse into PrintNode's (thanks to Gero).
* Mark undeclared variable usage as such and not as undefined.
implementing execute button for gui
Merge branch 'master' into gui
The GUI can now execute the LLVM code generated by the compiler.
Also a bug was fixed in the controller. The controller did not abort execution when the reportLog contained any errors.
modified all build scripts to include debug info in class files.
Implemented the Result View for the gui