Use different icons to indicate when friends are online/offline

[DarkGradient]

Because for now, it looks like - someone deleted me from friend list, or added me. I think, instead of - and + this should be dot.

[peppy]

Some proposals:

[peppy]

faces:

diff --git a/osu.Game/Online/FriendPresenceNotifier.cs b/osu.Game/Online/FriendPresenceNotifier.cs
index dd141b756b..eee04a749c 100644
--- a/osu.Game/Online/FriendPresenceNotifier.cs
+++ b/osu.Game/Online/FriendPresenceNotifier.cs
@@ -169,7 +169,7 @@ private void alertOnlineUsers()
 
             notifications.Post(new SimpleNotification
             {
-                Icon = FontAwesome.Solid.UserPlus,
+                Icon = FontAwesome.Solid.GrinBeam,
                 Text = $"Online: {string.Join(@", ", onlineAlertQueue.Select(u => u.Username))}",
                 IconColour = colours.Green,
                 Activated = () =>
@@ -204,7 +204,7 @@ private void alertOfflineUsers()
 
             notifications.Post(new SimpleNotification
             {
-                Icon = FontAwesome.Solid.UserMinus,
+                Icon = FontAwesome.Solid.Dizzy,
                 Text = $"Offline: {string.Join(@", ", offlineAlertQueue.Select(u => u.Username))}",
                 IconColour = colours.Red
             });

slash:

diff --git a/osu.Game/Online/FriendPresenceNotifier.cs b/osu.Game/Online/FriendPresenceNotifier.cs
index dd141b756b..2c0ce7578f 100644
--- a/osu.Game/Online/FriendPresenceNotifier.cs
+++ b/osu.Game/Online/FriendPresenceNotifier.cs
@@ -169,9 +169,9 @@ private void alertOnlineUsers()
 
             notifications.Post(new SimpleNotification
             {
-                Icon = FontAwesome.Solid.UserPlus,
+                Icon = FontAwesome.Solid.User,
                 Text = $"Online: {string.Join(@", ", onlineAlertQueue.Select(u => u.Username))}",
-                IconColour = colours.Green,
+                IconColour = colours.GrayD,
                 Activated = () =>
                 {
                     if (singleUser != null)
@@ -204,9 +204,9 @@ private void alertOfflineUsers()
 
             notifications.Post(new SimpleNotification
             {
-                Icon = FontAwesome.Solid.UserMinus,
+                Icon = FontAwesome.Solid.UserSlash,
                 Text = $"Offline: {string.Join(@", ", offlineAlertQueue.Select(u => u.Username))}",
-                IconColour = colours.Red
+                IconColour = colours.Gray3
             });
 
             offlineAlertQueue.Clear();