GUI: updated ReCaptcha workflow

- Updated ReCaptcha widget, which was unable to set keyDown event
  on it's input. Now it uses GWT's TextBox instead of Google's.
  Original input is hidden by CSS in ApplicationForm.css file.
- User can now submit ReCaptcha value by Enter key.

- Implemented default action focusing on all Confirm based dialogs.
  Default action is cancel (if both buttons are present) or ok, if
  only one button is present. Focus preference can be set manually
  before displaying (like for error report widget, where 'submit'
  is considered default).
Merge pull request #251 from zlamalp/recaptcha

GUI: updated ReCaptcha workflow & Confirm widget button focus