Panels: refactoring panel meta model & menu, will open up panel specific menu actions

src/css/less/panel.less

@@ -93,6 +93,10 @@
       border: none;
     }
   }
+
+  .dropdown-menu {
+    text-align: left;
+  }
 }
 
 .panel-highlight  {

src/css/less/variables.dark.less

@@ -146,7 +146,7 @@
 
 // Dropdowns
 // -------------------------
-@dropdownBackground:            @grafanaTargetFuncBackground;
+@dropdownBackground:            @heroUnitBackground;
 @dropdownBorder:                rgba(0,0,0,.2);
 @dropdownDividerTop:            transparent;
 @dropdownDividerBottom:         #222;