Allow using tool data bundles as inputs to reference data select parameters

[mvdbeek]

Enables galaxyproject/idc#36, and we could later allow users to generate (or just upload) bundles.

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• This is a refactoring of components with existing test coverage.
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[mvdbeek]

So ... this works for what we need in a first step. I guess these are the question marks I still have in my head:

• do we want a specific datatype for bundles that is distinct from data_manager_json ? I'm simply checking that the file size is different from the total size (which it is if there is bundle data), but this might be a little cleaner
• we're persisting {"src": "hda", "id": 1} as the parameter value for the select parameter (instead of the value string). I think we could make that a little cleaner if we modeled this as a union between a select parameter and a data input parameter. We don't have such a concept now though, and maybe that's separate work ? It would let us specify mutually exclusive parameters eventually though, which could be cool. Maybe this would also formalize the map-over / not mapped over distinction ? idk
• should we make bundles uploadable ? this would be a really nice way to provide test data with iwc workflows, we could rework tool tests in a way that makes the tests runnable against non-managed instances (i.e. real server where you can't just mess with reference data). In a sense this would even make the cvmfs data more accessible to folks who can't mount cvmfs, since you could just reference the datacache url ...

[jmchilton]

Amazing - thanks so much! I guess it needs a rebase.