adding feature to click inside menu and not close it

Hey, I implement a feature in a project of mine that I believe would be a good extra feature for your great module.

I wanted to use your context menu within an input and update that value before closing the menu, in other words, I wanted to be able to click the input field and keep the menu opened.

In order to use this feature you have to add data-keep-opened="class-opened" to the element containing context-menu directive.

You also need to add the class "class-opened" to the element inside the context menu that you don't want to be closed when clicked on.

Usage example:

```html
<div context-menu data-keep-opened="class-opened" data-target="myMenu">

<div class="dropdown position-fixed" id="myMenu">
  <ul class="dropdown-menu">
    <li>
      <input type="text" ng-model="model.name" class="class-opened" />
    </li>
  </ul>
</div>

```

Working Plunkr with example:
http://plnkr.co/edit/a8QNKfxSN7p0a9SE10EC?p=preview

I hope this adds value to your great module.

Please let me know if you have any questions.
Gustavo