Make Documentation Viewer Accessible Throughout GUI

[tsole0]

Description

Makes the documentation viewer more accessible throughout the entire GUI.

Instead of requiring the documentation viewer widget to be a child of GuiManager, it now has no parent. However, it remains open until it is closed or SasView is closed because it is assigned to a class variable of the GuiManager class, which is always open. If there is already a documentation viewer open, a new (or old but unused) class variable is generated to store the new instance of the documentation window.

Additionally, this allows the GPU preferences Help button to be directed to a documentation viewer instead of being sent to a website. Fixes #2952 and resolves the remaining work from #2909.

How Has This Been Tested?

Tested opening multiple documentation windows together; windows from different parts of the program; and windows that send to pages with section references (#'s).

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)

Licencing (untick if necessary)

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

[tsole0]

I don't know of any other places in the GUI whose help buttons are being sent to a web browser instead of the documentation viewer, but if there are any that I missed those fixes should be included in this PR.

[krzywon]

I made a few suggestions to clean up the code. I tested the functionality and multiple windows are opened, but you should ensure all windows call the new method. The OrientationViewer is still sending the help to the web browser. I would suggest you look for the webbrowser import.