Configuration file format

[ntessore]

I would like to go to a configuration file format that is

• more explicit in the definition of source planes, and
• easier to read when there are many lenses and sources.

For the first point, I think it is important that the lenses and sources on a plane are grouped explicitly, and not implicitly by the order in which they appear.

The the ease of reading the file, it should be possible to specify priors directly at the point where objects are defined, instead of indirectly via identifier and parameter name. This could also get rid of the need to give everything a name that will usually end up being lens1, lens2, ..., lensN.