Implement relationships

[echus]

Define relationships between interface fields.

E.g.:

• Choice of fit method determines whether bounds are available on a parameter resource

[echus]

Notes from previous discussion:

SASVIEW 1 data: tabular data resource 2 fit method: string enum 3 form factor model: string enum 4 DEPENDENT on 3 - structure factor model: string enum 5 DEPENDENT on 3 - form factor params: params resource 6 DEPENDENT on 4 - structure factor params: params resource 7 fit details: tabular data resource

BINDFIT 1 data: tabular data resource 2 fit method: string enum (null, Nelder-Mead, L-BFGS-B) 3 fit model: string enum (nmr 1:1, 1:2, uv 1:1, etc) 3.5 fit model params: params resource 4 DEPENDENT on 3 (changes default value) - sub init values: boolean 5 DEPENDENT on 3 (changes default value) - dilution correction: boolean 6 DEPENDENT on 3 (only available on some models) - flavour: string enum (null, add, stat, noncoop) 7 fit details (will deal with these later)