Add All button in Complex Constraint window does not work for polydisperse parameters

[gonzalezma]

Describe the bug
The Complex Constrain interface allows setting automatically all the possible constraints between 2 FitPages. However, the polydisperse parameters are ignored.

To Reproduce
Steps to reproduce the behavior:

1. Load 2 data sets and define a model that includes PD params.
2. Go to the Constrained or Simultaneous Fit.
3. In Add constraints, set M2.scale = M1.scale and then press Add All.
4. See error:
   4.1 All the parameters of the model page are added to the list of constraints, e.g.:
   M2.scale = M1.scale
   M2.radius = M1.radius
   M2.thickness = M1.thickness
   BUT also non-fittable parameters (e.g. sld) are added to the list. This should probably be reconsidered.
   4.2 The PD parameters (e.g. radius.width) are not added, so they have to be included one by one.

Expected behavior
Only adjustable parameters should be added to the list of constraints when using the Add All button.
The adjustable PD params should also be added.

SasView version (please complete the following information):

• SasView 5.0.6? Tested in ESS_GUI_constrain_branch to be merged, as before it was not even possible to define constraints for PD parameters.

Operating system (please complete the following information):

• Windows 10

[gonzalezma]

Fixed by PR #2743