VelvetFeatureModelReader: set root as abstract and mandatory (fix #5), fix bug in getProject(); change directories (MPL -> Interfaces, Imports -> MPL), small fix in ConfigurationEditor for possible
later bug
Merge branch 'master' of github.com:OVGU-Teamprojekt-Velvet/FeatureIDE

Conflicts:
	plugins/de.ovgu.featureide.fm.core/src/de/ovgu/featureide/fm/core/io/velvet/VelvetFeatureModelReader.java
check for null project