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.
This is as many as seem safe. Lots inside mrlegacy that could be excluded but its all in the same artifact so leaving in unless someone knows how to exclude particular partial packages. 

Won't change the code to trim things from the classpath in this commit but I suspect the dependencies.jar may be all that is needed for spark-shell and drivers.

@andrewpalumbo there's little chance this will mess up your drivers so I may push this after some more testing on my side.