Add SasView version flag to model marketplace

[butler]

The point of the marketplace is to provide a forum for all SasView models to be publicly available and easily accessible without digging through the installation directories and/or the github tree. Also can serve as a repo for emerging efforts to have all code used in papers available as well as efforts to make commonly used routines and methods cataloged and easily available.

The issue arises when there is an API change to sasmodels. There have already been a couple and given the wishlists it may require another. Thus it is important that the code for each model be identified as to which version of the sasmodels (and thereby SasView) API it works with. Some design thought would probably be appropriate in terms of how to record the range of versions covered as well as how to present the potential plethora of each model (one for each API version).

[awashington]

I think that it might be worth having both the explicit flag and a bit of implicit verification. As an example:

Alice uploads a model for unoriented rabbits and flags that it works with sasmodels version 2.0. Bob has also uploaded a model for handling magnetic conga-line rabbits. Sasmodels version 3.0 makes a breaking change in the handling of oriented magnetic particles, which doesn't effect Alice's code at all, but completely breaks Bob's code. Alice and Bob have both finished their degrees and haven't updated the flags in the marketplace. Eve wants to use both models, but is on Sasmodels 3.0. The marketplace should be able to tell her that Eve's code is probably broken, since it's calling an old api, but should still provide her with Alice's code, since none of that has changed.