Configurable supermajority requirements related to "disqualification" of initiatives for stability reasons

- Added columns "no_multistage_majority" and "no_reverse_beat_path" to table "policy"
- Renamed columns "(un)favored" to "(un)favored_to_status_quo"
- Renamed "preliminary_rank" to "schulze_rank"
- "schulze_rank" may have a gap due to status quo
- Renamed column "disqualified" to "multistage_majority" in table "initiative"
- Added column "reverse_beat_path" to table "initiative"
- Added column "eligible" to table "initiative"
- Removed column "final_rank" from table "initiative"
- Modified function "calculate_ranks" to fit above changes