Add "Copy Link Address" context menu

Allows copying just the link address of a hyperlink.

src/timeline/Bubble.qml

@@ -78,6 +78,11 @@ QQC2.Control {
      */
     signal selectedTextChanged(string selectedText)
 
+    /**
+     * @brief The user hovered link has changed.
+     */
+    signal hoveredLinkChanged(string hoveredLink)
+
     /**
      * @brief Request a context menu be show for the message.
      */
@@ -108,6 +113,9 @@ QQC2.Control {
                     onSelectedTextChanged: selectedText => {
                         root.selectedTextChanged(selectedText);
                     }
+                    onHoveredLinkChanged: hoveredLink => {
+                        root.hoveredLinkChanged(hoveredLink);
+                    }
                     onShowMessageMenu: root.showMessageMenu()
                     onRemoveLinkPreview: index => root.contentModel.closeLinkPreview(index)
                 }