Scalatra + swagger

Makes it easy to integrate Sumac args with Scalatra, and get swagger docs from the Sumac definitions.

Everything isn't supported yet, but its a decent start -- primitives, `DateTime`, and collections of those.  It actually wouldn't be too hard to generate swagger docs directly from sumac, and skip scalatra completely (eg., if you want to use w/ unfiltered).
this is the whole point of the PR.  You just put your arg type as a parameter, and this automatically
* parses out the path & query params for you (with error handling)
* generates swagger docs based on the arg type