Introduce groups/collections/projects for a series of calculations

[jthorton]

Description
Keeping track of groups of calculations is difficult as each molecule has an assigned id and tracking many of these becomes confusing. Instead, we could add the ability to store calculations under a group or collection name similar to what is done in QCFractal. This way molecules for one project can easily be pulled from the server by supplying the group/collection/project name this will help with tasks like listing the progress of a group of calculations or collecting the results from a group of calculations.

I don't think we need to extend the schema to track the project though we certainly could, instead I think we can just store lists of task ids against collection names in the redis db (a dict of lists) and look up the ids associated with the collection when needed.