Fix item type icons broken on 2x screens

Icons preloading introduced in 247755c5 overrides entire background
property, not just background-image. On 2x screens (and anywhere else
where svg icons need to be scaled) icons need property `background-size:
contain` to be displayed correctly. This previously came from
`.icon-css` class but have been overriden by code generated in
`svgicon`, so to fix this, these properties need to be added to the
`svgicon`.

scss/abstracts/_svgicon.scss

@@ -1,6 +1,6 @@
 @mixin svgicon($icon, $color, $size: "16", $prefix: false, $has2x: false) {
     background:
-        -make-icon-background($icon, $color, $size, $prefix, $has2x),
+        -make-icon-background($icon, $color, $size, $prefix, $has2x) no-repeat center/contain,
         
         // Invisible backgrounds to preload all variants:
         -make-icon-background($icon, 'white', $size, $prefix, $has2x) center/0,

scss/components/_icons.scss

@@ -14,9 +14,6 @@
 
 .icon-css {
   display: inline-block;
-  background-repeat: no-repeat;
-  background-size: contain;
-  background-position: center;
   vertical-align: middle;
 }