Refactor editing ux

[sneridagh]

Bugs:

• form title and description are not rendered
• Choice and Multiple Choice fields:
  • can't enter choices (currently pressing Enter propagates outside the modal)
  • can't validate input (currently the choices aren't in the schema in the format expected by the Python jsonschema validator)
• make all the captcha widgets work (currently only honeypot does)
• fix failing tests (mostly related to captchas)
• fix lint errors

Cleanup:

• remove old form block
• rename packages

Features:

• custom (preset) fields
• thank you / confirmation settings
• field types
  • render Multiple Choice as checkboxes
  • Single Choice
  • Time
  • Numeric
• mailer features
  • Administration Info
  • Fixed Attachment
  • Template

[mamico]

@davisagli as anticipated verbally, we would need the backend package to still have setup.py, at least until PEP 660 is fully implemented in zc.buidlout (see buildout/buildout#652)