Default width of main column to 50%

This will later be controled by draggin the col-splitter

src/styles/_base.sass

@@ -57,6 +57,7 @@ nav.sidebar
 #col_main
 	background-color: white
 	border-right: thin solid $color-background-dark
+	width: 50% // gets overriden by JS, dragging the col-splitter
 
 #col_right
 	background-color: $color-background-light