Permissions changes for educators and researchers

[kjdav]

-allow researchers to add/edit local labels to assignments (to do this, do we have to give them the ability to edit assignment plans? if so, that is not ideal but seems an ok trade-off)

-allow researchers to add/edit global labels

• if an instructor marks "no this is not an experiment" -- seems like we should hide cohorts and consent. most instructors won't use these options and it is a bit confusing to have them there. consent is nbd, but cohorts could be a bit dangerous if someone adds cohorts and/or links sections improperly.