Add frontend and API support for deleting tags. Model support is needed.

static/css/quay.css

@@ -1148,6 +1148,34 @@ p.editable:hover i {
   font-size: 1.15em;
 }
 
+#tagContextMenu {
+  display: none;
+  position: absolute;
+  z-index: 100000;
+  outline: none;
+}
+
+#tagContextMenu ul {
+  display: block;
+  position: static;
+  margin-bottom: 5px;
+}
+
+.tag-controls {
+  display: inline-block;
+  margin-right: 20px;
+  margin-top: 2px;
+  opacity: 0;
+  float: right;
+  -webkit-transition: opacity 200ms ease-in-out;
+  -moz-transition: opacity 200ms ease-in-out;
+  transition: opacity 200ms ease-in-out;
+}
+
+.tag-heading:hover .tag-controls {
+  opacity: 1;
+}
+
 .right-title {
   display: inline-block;
   float: right;