Add "Show only unread" checkbox

[berkus]

Show only unread chats when this is enabled;

for quick on/off place it somewhere reachable - e.g. a simple checkbox next to the Search bar.

[webreh]

I think this should be either an option for chat notifications (no notify & hide) or a special search filter

[berkus]

A ☑️ may work as a filter, indeed.