Show different colors based on filled value

This shows green until the bar is at 50%, yellow until 33%, and red
below that.

This also fixes the bar to show white when "colored" is disabled in the
config.

screenlogic.css

@@ -118,7 +118,7 @@
     line-height: 20px;
     color: #fff;
     text-align: center;
-    background-color: #337ab7;
+    background-color: #fff;
     -webkit-box-shadow: inset 0 -1px 0 rgba(0,0,0,.15);
     box-shadow: inset 0 -1px 0 rgba(0,0,0,.15);
     -webkit-transition: width .6s ease;
@@ -128,4 +128,12 @@
 
 .MMM-ScreenLogic .progress-bar-success {
     background-color: #5cb85c;
+}
+
+.MMM-ScreenLogic .progress-bar-warning {
+    background-color: #ffc107;
+}
+
+.MMM-ScreenLogic .progress-bar-danger {
+    background-color: #dc3545;
 }