Use SBT's managed dependencies for NER libraries

Dependencies of NER Tools (only Linnaeus at the moment) were managed manually
by placing its JAR files inside the "/lib" directory; now they are managed by
the SBT library resolver, by using a couple of Maven repositories holding them.
It will probably be a good idea (that will not be done in a nearby future) to
have a self-hosted maven repository for them.

With this change, dependencies on ABNER and Oscar libraries have also been
added.