Always ensure stable voting results by disqualifying certain initiatives, and bugfix related to setting "issue_state" in "calculate_ranks"

- Removed column "majority_indirect" from table "policy"
- Removed column "eligible" from table "initiative" ("eligible" can be calculated as "attainable"=TRUE AND "favored"=TRUE AND "disqualified"=FALSE)
- Split "rank" column of table "initiative" into columns "preliminary_rank" and "final_rank"
- Added column "disqualified" to table "initiative"
- Removed column "promising" from table "initiative"
- Removed constraints from table "initiative"
- Updated functions "close_voting" and "calculate_ranks"
- Added TODO notice in function "clean_issue"