Update for SS4

[robingram]

@markguinn This makes the module compatible with SS4 but it will break it for SS3 so I suggest that before merging you should:

• Tag the current latest commit as a release, bumping a minor version number
• Create a branch from the current state in case you need to make changes to the SS3 version

And then after merging ideally tag another release, maybe bumping the major version number even.

Let me know if you spot any issues.

[sirtoobii]

hey @robingram, since @markguinn 's account seems to be inactive, would you mind releasing your fix(es) as a new package? Or if you're okay with it I could fork it to my companies @oposs organization account and create new release there?

[robingram]

Hey @sirtoobii, I haven't done any Silverstripe stuff for a while so if you want to fork my branch and take it from there then I'm more than happy for you to do that.