further implemented rekeying, added cleanup stoppable, and fixed race

context/networkManager.go

context/params/E2E.go

context/params/Unsafe.go

context/stoppable/cleanup.go

context/stoppable/multi.go

context/stoppable/single.go

network/keyExchange/confirm.go

network/keyExchange/init.go

network/keyExchange/rekey.go

network/keyExchange/trigger.go

storage/utility/cmixMessageBuffer.go

storage/utility/e2eMessageBuffer.go

storage/utility/e2eMessageBuffer_test.go

storage/utility/messageBuffer.go