Create boilerplate css code for navigation utilities, like delete and edit

:construction: 

Work in progress

Motivation for this is to ease the pain of creating and standardize often used actions for navigation entries, like editing the entry or deleting it. It allows to keep and evolve mobile styles in core.

* adding the **app-navigation-entry-loading** class to an entry replaces the background image with a loading icon:

    \<li class="app-navigation-entry-loading**>

 produces 
![loading](https://cloud.githubusercontent.com/assets/195053/4048639/a3bc01c8-2d45-11e4-98ea-c262e35d64f3.png)

* app utilities are added like this after the link:

 ```html
<li>
    <a>The title</a>

   <!-- utilities -->
    <div class="app-navigation-entry-utils">
        <ul>
            <li class="app-navigation-entry-utils-counter"
                ng-show="feed.id && Navigation.getUnreadCount(feed.id) > 0 && !feed.error && !feed.editing">
                {{ Navigation.getFeedUnreadCount(feed.id) | unreadCountFormatter }}
            </li>
            <li><button class="app-navigation-entry-utils-menu-button" ng-click="optionsId = (optionsId == feed.id ? -1 : feed.id)"></button></li>
        </ul>
    </div>

    <div class="app-navigation-entry-options" ng-class="{'app-navigation-entry-options-open': optionsId == feed.id}">
        <ul>
            <li><button class="icon-rename" title="<?php p($l->t('Rename feed')); ?>"></button></li>
            <li><button class="icon-delete" title="<?php p($l->t('Delete website')); ?>"></button></li>
        </ul>
    </div>
```

 produces 
![utils](https://cloud.githubusercontent.com/assets/195053/4048676/fdbebf9e-2d45-11e4-884a-0bfb1d7e5553.png)

**TODO**:
* [ ] Provide class to allow adjusting the ellipsis for each item depending on if a counter is also used
* [ ] Provide styling for inputs if you want to edit an entry
* [ ] Create developer documentation 

@jancborchardt @MorrisJobke @georgehrke @DeepDiver1975 @LEDfan @raghunayyar