feat(header): apply shadow on MD headers

src/components/toolbar/toolbar.md.scss

@@ -29,6 +29,19 @@ $toolbar-md-button-border-radius:        2px !default;
 $navbar-md-height:                       $toolbar-md-height !default;
 
 
+ion-header::after {
+  // using datauri png background image for improved scroll performance
+  // rather than using `box-shadow: 0 2px 5px rgba(0,0,0,0.26);`
+  // noticable performance difference on older Android devices
+  position: absolute;
+  width: 100%;
+  height: 5px;
+  content: '';
+  background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABgAAAAIBAMAAAARjyJQAAAAFVBMVEUAAAAAAAAAAAAAAAAAAAAAAAAAAAASAQCkAAAAB3RSTlMBLRUGDSA4cBS/RQAAACBJREFUeF5jSEMCDIJIgCEUCTAoIQEGFyTAYIwEGHACAG7+EL36X1OAAAAAAElFTkSuQmCC);
+  background-repeat: repeat-x;
+}
+
+
 .toolbar {
   padding: $toolbar-md-padding;