refactor(live-update)!: remove setChannel and getChannel

[robingenz]

The setChannel and getChannel seems to confuse many developers. There have been several support requests where the problem was that setChannel was called too late or not at all and thus no live update was received.

-> Therefore both methods should be replaced by a new channel parameter in the sync(...) method.

[riderx]

Same problem in mine, that was the first naive way of doing it ^^