updated tests
updated bdd defaults
update FeatureModelFactory interface

 * allow user-defined variable-name prefix instead of hard-coded CONFIG_
 * better error message on failed assert
improve FeatureExprParser

* supports now also atMostOne
* oneOf is implemented more efficiently
* allows to parameterize how to recognize feature names
* supports prefixes for feature names
workaround for Scala-Java interaction with default parameters
remove unnecessary file
remove compiler warning
untrack .idea files
merging master
cfg error reporting to stdout instead of tmp-files; preparation for jenkins