* rename hasAccess to canJoin for challenges
This is so the function won't be used accidentally for other
purposes, since hasAccess could be misinterpretted.
* add isLeader function for challenges
* allow challenge leader to join/modify/end challenge when they're not in the private group it's in
* delete duplicate test
* clarify title of existing tests
* add tests and adjust existing tests to reduce privileges of test users
* fix lint errors
* remove pointless isLeader check (it's checked in canJoin)
Alys
eb2d320d1f