Several changes in "Harvest sources" page and the related action bean:
- Use DisplayTag instead of subjectsResultList.jsp
- use Enum for tabs, as opposed to constants
- mark priority sources with light red flags next to checkboxes
- remove "Schemas" tab, as inference is no longer used
Also removed "Is schema source" flag in source add/edit/view page, as it was useless.
Refs #3559.