Added setting and functionality to highlight inline whispers

Inline whispers will be displayed with highlighted background color.

New Flag needed to differentiate between normal whisper (highlighted) and whisper with mention.

src/messages/Message.cpp

@@ -21,7 +21,8 @@ Message::~Message()
 
 SBHighlight Message::getScrollBarHighlight() const
 {
-    if (this->flags.has(MessageFlag::Highlighted))
+    if (this->flags.has(MessageFlag::Highlighted) ||
+        this->flags.has(MessageFlag::HighlightedWhisper))
     {
         return SBHighlight(SBHighlight::Highlight);
     }