Reorganises Shape2SAS UI for plots

[jellybean2004]

Description

Changes the layout of plots in the tool window to be tabbed instead of vertically stacked to give plots more space.

Also reformats and cleans up some of the code in the changed files.

Fixes #4044

How Has This Been Tested?

Manually tested.

Review Checklist:

Documentation

• There is nothing that needs documenting
• Documentation changes are in this PR -- will add as final commit after design finalised.
• There is an issue open for the documentation

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

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

[jellybean2004]

The new commit adds a third tab, which shows both the viewer and the scattering profile vertically stacked.

Instead of creating duplicates, the tabs reuse the plots.