Rename Keys.Room.(previous/next)_urgent setting

to (previous/next)_highlight, to match the new terminology used from the
previous notification settings commit.

src/config/settings.py

@@ -303,10 +303,12 @@ class Keys:
         previous_unread = ["Alt+Shift+U"]
         next_unread     = ["Alt+U"]
 
-        # Switch to the previous/next room with urgent messages in the list,
-        # e.g. messages mentioning your name, replies to you or keywords.
-        previous_urgent = ["Alt+Shift+M"]
-        next_urgent     = ["Alt+M"]
+        # Switch to the previous/next room with highlighted messages in the
+        # list. What causes a highlight is controlled by push rules
+        # (editable in GUI account settings): by default, this includes
+        # when your name is mentioned, replied to, or messages with keywords.
+        previous_highlight = ["Alt+Shift+M"]
+        next_highlight     = ["Alt+M"]
 
         class AtIndex:
             # Switch to room number X in the current account.

src/gui/MainPane/RoomList.qml

@@ -264,12 +264,12 @@ HListView {
     }
 
     HShortcut {
-        sequences: window.settings.Keys.Rooms.previous_urgent
+        sequences: window.settings.Keys.Rooms.previous_highlight
         onActivated: cycleUnreadRooms(false, true) && showItemLimiter.restart()
     }
 
     HShortcut {
-        sequences: window.settings.Keys.Rooms.next_urgent
+        sequences: window.settings.Keys.Rooms.next_highlight
         onActivated: cycleUnreadRooms(true, true) && showItemLimiter.restart()
     }