added admin interface

admin/assets/scss/mixins/_responsive.scss

@@ -0,0 +1,19 @@
+// mixins for mobile responsiveness
+
+@mixin screen($res-min, $res-max) {
+	@media screen and ( min-width: $res-min ) and ( max-width: $res-max ) {
+		@content;
+	}
+}
+
+@mixin max-screen($res) {
+	@media screen and ( max-width: $res ) {
+		@content;
+	}
+}
+
+@mixin min-screen($res) {
+	@media screen and ( min-width: $res ) {
+		@content;
+	}
+}