Exp. Versioning: Model Changes

[stephherbers]

Model changes for Experiments, Source Material, and Safety Layers. Takes as much or start over from this PR

Note the decision to use bools rather than a "status" field:
class Experiment:
working_experiment = FK
version_number = int
default = bool
archived = boo

(For Source Material, and Safety Layers we want it to function like the Experiments we discussed where there is a "working" field that is empty for non-copies)

[SmittieC]

Done