Remove unused imports that point at deprecated ConcurrentMap

The ConcurrentMap is gone in 2.11.
Add conditional dependency on scala-parser-combinators module.

If Scala 2.11 is used to compile the project, add newly spawned
scala-parser-combinators module as a dependency.
Update sbteclipse plugin to 2.4.0 version.
Merge pull request #92 from gkossakowski/scala-2.11

Scala 2.11 compatibility