1.2.4: Field name selector improvements

Backend

• New API endpoint to check the validity of a field name with IntelMQ.

Frontend

• Updated dependencies: babel/traverse, browserify-sign
• Mail parser: handle multi-line subject/to
• yarn.lock: re-resolve all packages
• Field name drop downs:
  • prevent overflows
  • add wrapping and reduce paddings
  • improve visibility of action buttons
  • check the validity of an entered field name with IntelMQ
• validate checkbox: show reason if no bots available
• other minor improvements

Documentation

• minor changes