Fetch 1.7.0-SNAPSHOT from ukp-public-snapshots

The user doesn't have to build the dkpro from svn on their own anymore.
Kindly suggested by Richard Eckart.

It is a little problematic since our build is not reproducible right now
and changes in dkpro before 1.7.0 may randomly affect our performance.
However, the memory savings are too massive and tempting, given that
1.7.0 release is planned for November which isn't so far away.
BerkeleyParser: Remove our own implementation

We don't use it anymore, so let's not include foreign namespace classes
if we can avoid it; for anyone who wants to switch, perhaps new dkpro
versions can handle this already, or they can resurrect this from the
git history.
desc.type.Constituency.xml: Remove, not needed anymore