Support dynamic enabling and disabling of controls

See documentation in README for how this works. This commit
handles all the main controls. Pads are not yet supported.

data/css/style.css

@@ -422,7 +422,7 @@ button {
   background-color: #999999;
 }
 
-button:active {
+button:enabled:active {
   background-color: #666666;
   transform: translateX(4px) translateY(4px);
 }
@@ -1148,3 +1148,46 @@ text {
 .vert-slider span {
   transform: rotate(90deg);
 }
+
+
+/* Styles to implement disabled controls */
+
+button:disabled {
+  color: #333;
+  background-color: #999;
+}
+
+select:disabled {
+  color: #333;
+  background-color: #999;
+}
+
+input:disabled {
+  color: #333;
+  background-color: #999;
+}
+
+.range-slider__range:disabled {
+  background-color: #999;
+}
+
+.range-slider__range:disabled::-webkit-slider-thumb {
+  background-color: #aaa;
+}
+
+.range-slider__range:disabled::-moz-range-thumb {
+  background-color: #aaa;
+}
+
+.switch.disabled .in::before {
+  background:#bbb;
+  border: 1px solid #ddd;
+}
+
+.switch.disabled .in::after {
+  background:#bbb;
+}
+
+.switch.checked.disabled {
+  background: #b1d092;
+}