Integration of Daniel's BLOB manager

I rebased the pull request #107 of @warneke. Thanks for your work Daniel, the code looks really good. Since the master evolved a little bit from the version of the pull request, I'd like to have another pair of eyes looking over it. I tried to address the problem of old jar files which are no longer used by introducing a clean up task which regularly looks for those files. Due to this I had to extend the book keeping of the LibraryCacheManager a little bit.

I tested WordCount and Kmeans on the cluster with this version.
Why change it from 2*cores to 3*cores?