Edit forms inline

[wwqrd]

• Form configuration is now part of particular interface where it is used
• Form fields are added inline, which automatically creates corresponding
  variable entries

Resolves #390

[wwqrd]

Demo/review feedback

• From the node type editor don't require minimum number of variables.
• "Prompt" should be a Text input
• Add /check guidance / descriptive text for new fields
• For form section, clearly link the title and fields: mini divider? box outline?
• Radio groups etc, should be able to add options
• Variable name isn't showing up in field editor for previously saved field.
• Field preview should be improved: variable name (e.g. "Name"), variable type (as color). Perhaps as a "tag" style.
• scrolling with select react component not following, create new issue?
• TextArea max width (see field prompt), min-height, create new issue?

[wwqrd]

Text area issue: complexdatacollective/Network-Canvas-UI#101

[wwqrd]

React select issue: https://github.com/codaco/Architect/issues/433

[wwqrd]

This looks done to me? @rebeccamadsen @jthrilly

I think the Options input (for radio group etc) could do with validations, but since that's a pre-existing component, I suggest we make that a separate PR.