Externalize pagination template

Externalizing the pagination template makes it possible to create custom pagination templates. If, for instance, you're using Foundation instead of Bootstrap (like in my case). You could define the following in your own project:
```
angular.module('ui-templates', ['smart-table']);
angular.module('ui-templates').run(['$templateCache', function($templateCache) {
  $templateCache.put('template/smart-table/pagination.html',
    '<div class="pagination-holder"><ul class="pagination" ng-if="numPages>1"><li class="arrow" ng-class="{unavailable: currentPage==1}"><a ng-click="selectPage(1)"></a></li><li class="arrow" ng-class="{unavailable: currentPage==1}"><a ng-click="selectPage(currentPage-1)"></a></li><li ng-repeat="page in pages" ng-class="{current: page==currentPage}"><a ng-click="selectPage(page)">{{ page }}</a></li><li class="arrow" ng-class="{unavailable: currentPage>=numPages}"><a ng-click="selectPage(currentPage+1)"></a></li><li class="arrow" ng-class="{unavailable: currentPage>=numPages}"><a ng-click="selectPage(numPages)"></a></li></ul></div>');
}]);
```