Added start position to collection repeat

Because collection repeat is absolute, you couldn't put something before
it.
Added "collection-start-pos" attr to change the start position of the
list, so you can put something before it.

Code Example - search bar before collection list : 
```html
<div class="list">
            <div id="search-box" class="bar bar-header item-input-inset">
                <div class="item-input-wrapper">
                    <i class="icon ion-ios7-search placeholder-icon"></i>
                    <input type="search" placeholder="search" ng-model="query">
                    <img class="clear-search" src="img/x.png" ng-click="clearSearch()">
                </div>
            </div>
            <a class="item my-item"
               collection-repeat="word in words"
               collection-item-height="70"
               collection-item-width="'100%'"
               collection-start-pos="44">
               {{word.text}}
            </a>
</div>
```