narrow: Explicitly resume the reading state when `narrow.deactivate`.

Previously, when a user marks messages as unread in the all messages view
then enters another view and finally back to the all messages view, they'd
notice that the reading state in all messages view is still paused. 

This happened uniquely for "All messages" because we only resumed the "reading"
state in `narrow.activate` (and generally that would generate a new MessageList anyway); 
but `message_lists.home` is a singleton, so the "no longer reading" state would remain
attached to that object forever.

Fix this by explicitly resuming the reading state when we enter all messages
view/message_lists via narrow.deactivate.

web/src/narrow.js

@@ -1064,6 +1064,7 @@ export function deactivate(coming_from_recent_topics = false) {
     $("#zfilt").removeClass("focused_table");
     $("#zhome").addClass("focused_table");
     message_lists.set_current(message_lists.home);
+    message_lists.current.resume_reading();
     condense.condense_and_collapse($("#zhome div.message_row"));
 
     reset_ui_state();