Universes and members should be locateable by relative paths.

[dotsdl]

At the moment, Universes and Members use only stored absolute paths for finding the files they need to generate universes and members, respectively. Relative paths from the Container's basedir are also stored, but they are not yet used. This breaks functionality for Sims and Groups when moving them around in a filesystem, even when the relative paths between these Containers and the files they require haven't changed.

The relative paths should be tried in the event the absolute path fails. If the file is found, the absolute path should be updated.

[dotsdl]

Eventually, the MDSynthesis.core.filesystem.Foxhound object will be used to sniff out missing members of Groups, but we shouldn't need to invoke it if such members can already be found by the Group with the information it already has.

[dotsdl]

Been hacking on this today, and after some significant changes to the GroupFile and Members aggregator it's become clear that a reasonable solution practically requires Foxhound to be implemented at a basic level before this issue can be resolved. I think this should happen before the 0.5.0 release, too, so the release might need pushing back.

[dotsdl]

Finally finished (mostly) an overhaul of Group.Members and Bundle that includes automatic hunting and finding of Containers that have moved. The Foxhound object handles the details of this filesystem search. After I add some explicit tests of this work I'll merge it into develop.

[dotsdl]

Merged into master the work that makes Group members locateable automatically by relative paths, as well as some brief period of searching if they can't be found. Still need to include a bit of code in Foxhound to make relative paths usable by Sim to find topologies/trajectories.