2889: Fitting Optimizer Broken After Load Project Fix

[krzywon]

Description

When projects are loaded, all perspectives are closed and regenerated to allow a completely fresh start. In this process, the perspective-specific preference widgets were not being renewed, orphaning their signals. This ensures the preference panel is recreated during this process.

Fixes #2889 (Maybe...?)

Side note - If approved in time, I may test this on the 6.1.3 release branch.

Review Checklist:

Documentation (check at least one)

• There is nothing that needs documenting
• Documentation changes are in this PR
• There is an issue open for the documentation (link?)

Installers

• There is a chance this will affect the installers, if so
  • Windows installer (GH artifact) has been tested (installed and worked)
  • MacOSX installer (GH artifact) has been tested (installed and worked)
  • Wheels installer (GH artifact) has been tested (installed and worked)

Licensing (untick if necessary)

• The introduced changes comply with SasView license (BSD 3-Clause)