4302 edit nodes containing data

[veuncent]

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Description of Change

Allows editing nodegroups that contain data.

Issues Solved

This code has gone awol since it was first implemented in Arches 4.1.
Adding it again after consulting @chiatt

Checklist

• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[coveralls]

Coverage decreased (-0.002%) to 40.504% when pulling 6689883 on 4302-edit-nodes-containing-data into bd5dfec on master.

[chiatt]

Works as expected. Thanks @veuncent!

[chiatt]

Looks great!