Set interior structure by: total planet mass, radius

[nichollsh]

Reworks the methods by which the user can set the interior structure. Previously, they would specify the dry interior mass, and the interior models would be used to inversely solve for the interior radius.

This is now offset by the total volatile inventory, such that the user only has to specify the total planet mass. This is what would be probed by RV or TTV measurements, so it is much easier to specify for the user. Closes #269.

Additionally, the user can avoid the whole mass -> radius conversion by setting the interior radius directly in the configuration file. Closes #267.

The physical test (which uses Aragog) now sets the structure using the planet radius (hence the test updates). The dummy test (which uses the Dummy interior) sets the structure using the total planet mass.

Minor things:

• AGNI has been updated to 0.11.0, which replaces the reset_vmr flag with the more obvious rainout flag. This PR includes a minor change to handle this accordingly.

[nichollsh]

Thanks a lot, @timlichtenberg! We should definitely look into this structure stuff more deeply, but I think that this is better than the previous implementation of over-specifying the mass and radius.