Make tracks in track admin sortable

• Add dragula dependency
• Apply to track admin
• Fix layout issues in track admin
• This implements #190 (closed)

AKScheduling/static/AKScheduling/vendor/dragula/dragula.css

+.gu-mirror {
+  position: fixed !important;
+  margin: 0 !important;
+  z-index: 9999 !important;
+  opacity: 0.8;
+  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=80)";
+  filter: alpha(opacity=80);
+}
+.gu-hide {
+  display: none !important;
+}
+.gu-unselectable {
+  -webkit-user-select: none !important;
+  -moz-user-select: none !important;
+  -ms-user-select: none !important;
+  user-select: none !important;
+}
+.gu-transit {
+  opacity: 0.2;
+  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=20)";
+  filter: alpha(opacity=20);
+}