Custom field HTML should indicate group+field name

Several forms used in CiviHR are generated as profile-forms with custom-data. These forms have HTML elements (<INPUT>, <SELECT>, etc) with the attribute "name=custom_X" (where X varies from system to system). This makes it hard to work with programmatically – for example, it is difficult to write JavaScript UI's and automated web-tests. To improve this, we should add more markup to the HTML elements, e.g.

<INPUT name="custom_X" data-crm-custom="TheCustomGroup:TheCustomField" />
<SELECT name="custom_X" data-crm-custom="TheCustomGroup:TheCustomField">...</SELECT>

where "TheCustomGroup" and "TheCustomField" correspond to the values in civicrm_custom_group.name and civicrm_custom_field.name (respectively). This will enable one to write selectors like:

cj('[data-crm-custom="TheCustomGroup:TheCustomField"]').val('new value')

The function CRM_Core_BAO_CustomField::addQuickFormElement() is responsible for reading a $field (DAO) and producing its HTML form-elements. This is probably the place to patch. (Aside: CRM_Core_BAO_UFGroup::buildProfile is also important in generating profile forms, but I don't think it has any direct impact on the markup used for custom-fields.)