Feature-Request: Radio-Button Settings

[sebastian-marinescu]

I would like to be able to use radio-inputs for some settings.
In my opinion that would be useful for little "switch-settings" like for example "enable/disable custom scrollbar".
Also, as currently I am using dropdowns for these two options, this would save the user 1 click :-)

As Mark attempted in #176 with the multi-select checkboxes, I also ran into the same JS-issue.
Jako also stumbled upon the exact same issue modxcms/revolution#12177 some time ago.

I will prepare a PR for my own feature-request here, and I am attempting a PR on the actual issue in the MODX code.