Simplify repetitive form code

[lindapaiste]

Background:
In forms which use react-final-form we have a lot of repeated boilerplate. For example every field has the same error code:

{field.meta.touched && field.meta.error && (
  <span className="form-error">{field.meta.error}</span>
)}

Changes:

• Create UI component FormField for an input with a label and an optional error message.
• Create logic component FinalFormField which uses the Form component from the react-final-form package and passes the props from the generated field down to the FormField UI.
• Use this new FinalFormField component in forms:
  • AccountForm
  • LoginForm
  • ResetPasswordForm
  • SignupForm

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123