added verb: zijn
Every attribute is an unique attribute.
Added test for changing an association to attribute
Merge branch 'master' of https://github.com/ArjanO/AP-NLP
Changed attribute type to a Class<?>.
YUMLExport now supports attributes(+tests).

Refactored duplicated code in YUMLExport:
Inside the export method the exportSource will be used.
Added the verb "Zijn" to the verb list
Merge branch 'master' of https://github.com/ArjanO/AP-NLP

Conflicts:
	res/werkwoorden.csv