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.
But if the error message is too misleading, shouldn't it be the responsibility of the function throwing the exception to generate a meaningful error message instead of the job manager's?