MAHOUT-1636

Started out simplifying driver code and making changes to all drivers to support that. Then ran into the fat job.jar issue of MAHOUT-1636 so created a slimmed down version of the old job.jar by adding excludes to job.xml and changing the name to "dependencies.jar"

The new jar works for spark-itemsimilarity and spark-row-similarity but needs to be tested for the naive bayes drivers. 

The dependencies.jar still contains a lot of stuff from mrlegacy, some is in external projects, like jackson that can be excluded with this mechanism but also a lot of mahout code that is unneeded in this jar. This later case would require some other mechanism than a simple <exclude> clause in the assembly xml file.

I believe the new dependencies.jar is the only thing that needs to be on the classpath when running spark drivers or the spark-shell. I haven't changed this but it is a further refinement we can try.