Instead of packing the note for public user before passing it to
streams, the note is now either packed for the user the respective
stream belongs to (`mainStream`) or not packed at all and then packed
later (`notesStream`).
Because this is a new common task between different channels, a shared
implementation of packing a note from notesStream is created. This
implementation will simply skip a note if it is not visible to the user
that the channel belongs to.
Instead of just hiding specific fields, the entire note is hidden. This means
that metadata of the note such as who is the author, when was it sent are
completely hidden.
Johann150