SS5 update and fix for issue #194

[PixNyb]

Description

This pr includes support for ss5 and fixes #194

Manual testing steps

Issues

Pull request checklist

• The target branch is correct
  • See picking the right version
• All commits are relevant to the purpose of the PR (e.g. no debug statements, unrelated refactoring, or arbitrary linting)
  • Small amounts of additional linting are usually okay, but if it makes it hard to concentrate on the relevant changes, ask for the unrelated changes to be reverted, and submitted as a separate PR.
• The commit messages follow our commit message guidelines
• The PR follows our contribution guidelines
• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

[GuySartorelli]

The 4.x release line of this module already supports Silverstripe CMS 5.

Please remove all changes which are not related to the specific issue this PR aims to fix.
Please also target this PR to the 4.0 branch.

[GuySartorelli]

@PixNyb Are you still interested in getting this merged in?

If so, please make the requested changes above. If not, I will close this PR.

[GuySartorelli]

@PixNyb looks like you made some new commits, but you haven't addressed anything I said in #274 (comment)

I am going to close this PR - feel free to open a new one with only the relevant commits, targetting the correct branch.