added directive clickForContextMenu to assist in opening context menu on touchscreen devices

This adds a directive called clickForContextMenu which can be used on an element within another element with the contextMenu directive.
```
<div class="some-info" context-menu data-target="my-target" >
  <span ng-click="someDefaultOption">Here is some text</span>
  <i click-for-context-menu class="my-menu-icon pointer"></i>
</div>```
This way you can embed a sub-element anywhere within a contextMenu which acts as a button to open the menu on devices which don't easily support context menus.