[Cms/Panel] Unify fields between panel and backend

[distantnative]

• Panel

  • Field.mixin: split into multiple mixins ([Panel] Split Field.mixin into prop-specific mixins #277)
  • Textareafield: use counter boolean prop to decide whether to show counter or not
  • TextField: add & use counter prop

• Backend

  • Remove Autofocus where not used ([Form] Remove autofocus mixin #279)
  • CheckboxesField/RadioField: what's with the columns prop?
  • DateField: implement range prop (and maybe rename it too)
  • Text mixin: use string types/return types
  • InfoField: use text mixin
  • TagsField: implement accept prop
  • TextareaField
    • Remove Converter
    • autosize and multline props not supported
  • Textfield:
    • add missing props (spellcheck, pattern)