speed up chatlist

[r10s]

with #1358 (comment) we keep observers running in the chat view even when the chat is not on top (as on android) - this has the huge advantage, that the view is kept up to date when eg. the profile is opened and the back-button or -gesture is amazingly fast.

this saves the load-db call when the chatlist comes to view (only needed once on program start)

we should do the same for the chatlist, that should give the app a real speed boost :)

as the chatlist updates are even debounced, this change should be even more safe than for the chat view (which, however, is less often and shorted covered by another view).