added transparent panel option

src/app/features/panel/partials/panel.html

-<div class="panel-container">
+<div class="panel-container" ng-class="{'panel-transparent': panel.transparent}">
 	<div class="panel-header">
 		<span class="alert-error panel-error small pointer" config-modal="app/partials/inspector.html" ng-if="panelMeta.error">
 			<span data-placement="top" bs-tooltip="panelMeta.error">

src/app/partials/panelgeneral.html

@@ -10,6 +10,7 @@
 		<div class="editor-option">
       <label class="small">Height</label><input type="text" class="input-small" ng-model='panel.height'></select>
     </div>
+		<editor-opt-bool text="Transparent" model="panel.transparent"></editor-opt-bool>
   </div>
 </div>
 

src/css/less/panel.less

@@ -11,7 +11,7 @@
 }
 
 .panel-container {
-  background: @grafanaPanelBackground;
+  background-color: @grafanaPanelBackground;
   position: relative;
   border: @grafanaPanelBorder;
   &:hover {
@@ -19,6 +19,11 @@
       display: block;
     }
   }
+
+  &.panel-transparent {
+    background-color: transparent;
+    border: none;
+  }
 }
 
 .panel-content {