feat: setting added to enable/disable public access of wiki

[GSTbyMM]

All Submissions:

• Notify authors: @lastlink
• [NO] Have you updated the ChangeLog with your proposed changes?
• [YES] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• pr update to master branch
  • [NO] Have you updated the getPluginVersion() in Plugin.php?

New Feature Submissions:

• [YES] Have you added an explanation of what your changes do and why you'd like us to include them?

Description

Fixes # .

Changes proposed in this pull request:

• A setting has been added to enable/disable public access to the wiki