1726 allow user to choose default for plot navigation tools - merge into release_6.0.0

[juliuskarliczek]

Description

Same changes as mentioned in pull request #2845
Added documentation changes in preferences_help.rst as suggested in #2845

Added a checkbox in Preferences/Plotting Settings for using the matplotlib toolbar. Therefore edited the config and added USE_MATPLOTLIB_TOOLBAR.

Fixes # (issue/issues)
Fixes issue https://github.com/SasView/sasview/issues/1726 , where access to the standard matplotlib toolbar is requested.

How Has This Been Tested?

Local win10 build, tried plotting with and without the checked checkbox in the preferences. Both worked. Not sure, why the toolbar was disabled by default. Maybe that has to be checked.

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)

[krzywon]

Code review complete. I plan to test both the Mac and Windows installers later today.