Fix build by using unofficial non-PCL build of C5

I've included an unofficial non-PCL build of C5 in the lib folder. Unit tests pass on Linux now, with the exception of three tests that fail with

   System.IO.DirectoryNotFoundException : Could not find a part of the path "/home/greg/dev/MyMediaLite2/MyMediaLite/data/ml-100k/u1.base".

I assume I would need to get or generate that file somehow.