Add timeline_outline_width dimension in skin.xml

data/skins/default/skin.xml

@@ -12,6 +12,7 @@
     <dim id="tabs_icon_width" value="10" />
     <dim id="timeline_top_border" value="2" />
     <dim id="timeline_tags_area_height" value="4" />
+    <dim id="timeline_outline_width" value="2" />
   </dimensions>
 
   <colors>

src/app/ui/timeline.cpp

@@ -67,7 +67,7 @@
 // Space between icons and other information in the layer.
 #define ICONSEP         (2*guiscale())
 
-#define OUTLINE_WIDTH   (2*guiscale()) // TODO theme specific
+#define OUTLINE_WIDTH   (skinTheme()->dimensions.timelineOutlineWidth())
 
 // Space between the icon-bitmap and the edge of the surrounding button.
 #define ICONBORDER      0