* remove candidate when to invulnerable
* fix
* candidates to collators
* make parameters consistent and more reasonable
* add call to kick invulnerable candidates
* factor removal into weight
* fix: use accrue instead of add
* make set_invulnerables non-atomic
* benchmark add_invulnerable to account for candidate removal
* don't remove from candidates with set_invulnerables
* fix bounds on benchmarking
* protect against zero min invulnerables underflow
* extra event and tests
* make candidates/invulnerables self-cleaning on session change
* add integrity test
* unused imports
* make rococo-contracts have 1 collator