docs(changelog): transplant v0.7.8 notes from legacy-0.7 branch
docs(changelog): transplant v0.7.8 notes from legacy-0.7 branch

nodecg/nodecg,nodecg/nodecg,madmatt/nodecg,IgorCandido/igrcnddStreamNotifications,madmatt/nodecg,IgorCandido/igrcnddStreamNotifications,nodecg/nodecg