Add a Credits/Licences dialogue with relevant licence and copyright data

[llimeht]

Description

This PR achieves two things:

• it automates collection of the licence information for sasview when distributed in source, wheel, conda, etc form; this needs to be updated as part of the release process
• it automates collection of all licences when sasview is bundled with other packages such as in the pyinstaller-based installer images
• it displays these data via a dialogue box accessible from Help → Credits and licenses

As a future UI improvement, we might want to review and merge some of these help items into a tabbed dialogue but that's not necessary right now.

(This PR relies on an enhancement to src/sas/system/resources.py that are also proposed in #3678, so those 3 commits are also shown below)

Fixes #3095
Fixes #3477

How Has This Been Tested?

Running from a git checkout or from an installed wheel, Help → Credits and Licenses shows SasView, SasData and sasmodels licences.

Running from an installer, the dialogue will show the licences of everything that is bundled. (Noting that due to #3664, you have to delete sasmodels/models/two_yukawa.py for sasview to be able to start)

Review Checklist:

[if using the editor, use [x] in place of [ ] to check a box]

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)