Set "rank" for all "admitted" initiatives after voting is finished; Additional columns in "initiative" table store voting result information

Changes in detail:
- Renamed column "majority" of table "initiative" to "attainable"
- Added columns "favored", "unfavored" and "eligible" to "initiative" table
- Added constraints to "initiative" table, restricting certain value combinations in the the new columns
- Modified "calculate_ranks" function to update the new columns and always write "rank" information
- Marking the final winner is now done utilizing the new "eligible" column