Set ODS from ids objects

Leaf of #258. Allows an ODS to be set using an IDS (not database) object. Example syntax

ods = load_omas_imas(paths=omas_paths,
                                     imas_version=os.environ["IMAS_VERSION"], 
                                     ext_ids=ids)

with omas_paths a list of IMAS paths in the form of equilibrium.time_slice.0.profiles_2d.0.psi and ids in this case an instance of imas.equilibrium() with data. Limitations:

Does not allow automatic discovery, i.e. only works if paths is set
Does not allow broadcasting, e.g. equilibrium.time_slice.:.profiles_2d

gafusion / omas

Set ODS from ids objects #282