Data-driven USets

@IainNZ 
As we discussed.  This is in usable, although not perfect, shape...  I have a whole list of "To Do's" beore it would be perfect.  

Please take a look.  I have some specific questions on 
- How should we handle the package dependencies? For example, I require Roots.jl  but, base JuMPeR does not...
- See my current edit to the main Jumper.jl.  Is this the best way to do this?
- How should we loop the test suite into the main JuMPeR test suite?  Right now run_tests.jl covers the DDUSets  package using FactCheck
- Can I maintain a separate wish-list of desired features for DDUsets via the issues section of github? Or will it be naturally mixed into the JuMPeR issues?

Thanks so much, brother. 

Vishal
Whole file, yeah