SP-17: Bad JSON output when editing numbered-fields by hand

see JIRA: http://issues.gpii.net/browse/SP-17

As a workaround, the text-input fields have been marked as
'readonly'.
Merge remote-tracking branch 'javihernandez/SP-17'

* javihernandez/SP-17:
  SP-17: Bad JSON output when editing numbered-fields by hand