Fixes U4-4278 Multiple RadioButtonList on one Document

Manually applying pull request as it's a bit faster to copy&paste instead of resolve merge conflicts
Update version of ImageProcessor and refer to NuGet in the csproj instead of the bin (!)
Bump version number
Merge branch '7.1.0' of https://github.com/umbraco/Umbraco-CMS into 7.1.0