Implicitly use boolean AND for plain queries over all fields

See https://wiki1.hbz-nrw.de/display/SEM/NWBib-Treffen+10.9.2014
Fix regression in faceted search introduced by #64
Update to Play 2.3.4, Scala 2.11.2, and SBT 0.13.6
Fix issue in Travis config for running tests
Remove Scala source files from repo

Since this is a Play-Java application, we should not have Scala
source files in the project, as they require additional tools etc.

The custom Assets.scala was a leftover from running as a module,
the TagHelper.scala functions are now inside the template files.