MapR Tables (HBase) supported as Titan Backend

Here are my changes that were required to use MapR jar files.  I think they're unobtrusive, as you only use this with the 'mapr-m7' maven profile.

Also, there was a call to what I would characterize as unreliable modifyTable() in HBase.  This patch works with both MapR tables as well as Apache HBase, and is probably the solution to thinkaurelius/titan#165.