Count Selected Text Attribute

[slantz]

Added trivial realization of 'count-selected-text' attribute to be shown, when selected-text-format presents.

[lordfriend]

Would you please show me a demo for this feature?
According to the document of Bootstrap-select . This feature is for define the format of displayed text for toggle button when selectedTextFormat attribute is count>x or count. But your commit seems simply add the count-selected-text attribute into the button.
This wouldn't help for format the text.

In fact, there are a way to customize the format for selected-text-format.
See http://nya.io/nya-bootstrap-select/#!/api/nya-bs-config-provider

[slantz]

When modifying the provider in config method, it'd be applied globally across all the nya-bs-select elements. But in some cases it may be required to set particularly text for each element while keeping all other to behave as expected.

As an example I don't need to now the number of selected elements, some custom text is required when all elements are selected, e.g.

<ol class="nya-bs-select" ng-model="selectedItem" count-selected-text="All Cool Things" data-selected-text-format="count>{{items.length-1}}" multiple>
<li nya-bs-option="item in items">
<a>{{item}}<span class="glyphicon glyphicon-ok check-mark"></span></a>
</li>

</ol>

[lordfriend]

I think use data-binding in select-text-format attribute will fail. Your `count>{{items.length-1}} won't work.

But your commit doesn't make the feature fully functional as it described in Bootstrap-select. It just provide a text for, and will confuse the user who ever used the Bootstrap-select.