More context in doFill/doAutocomplete/doCheck

[Oliver Gondža]

I am implementing reusable describable to be used on multiple places on
config page (in multiple depths from json perspective) but need to refer
to several other inputs (on predictable json depth) its relative path
can be different.

I was ready to chop it out of the json or even request parameters but
none of that is available unless the form was submitted or the
parameters with (correct relative path) are explicitly stated in the
signature.

I ended up doing something like:

```
@RelativePath("..") @QueryParameter String myField,
@RelativePath("../..") @QueryParameter("myField") String myField2,
...
```

for every parameter. Needless to say this is awful, poorly scalable and
fragile. (Though it works surprisingly well, Stapler will actually
populate the parameters corresponding to the inputs not found with
values of those that were found!)

Is there any better way?
Thanks
--
oliver