chore(typeahead): change to one-way binding for position

- Change position to one-way binding to reduce an unnecessary $watch

chore(typeahead): add bind once to id attr

src/typeahead/typeahead.js

@@ -357,7 +357,7 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position', 'ui.bootstrap
         matches:'=',
         query:'=',
         active:'=',
-        position:'=',
+        position:'&',
         select:'&'
       },
       replace:true,

template/typeahead/typeahead-popup.html

@@ -1,5 +1,5 @@
-<ul class="dropdown-menu" ng-show="isOpen()" ng-style="{top: position.top+'px', left: position.left+'px'}" style="display: block;" role="listbox" aria-hidden="{{!isOpen()}}">
-    <li ng-repeat="match in matches track by $index" ng-class="{active: isActive($index) }" ng-mouseenter="selectActive($index)" ng-click="selectMatch($index)" role="option" id="{{match.id}}">
+<ul class="dropdown-menu" ng-show="isOpen()" ng-style="{top: position().top+'px', left: position().left+'px'}" style="display: block;" role="listbox" aria-hidden="{{!isOpen()}}">
+    <li ng-repeat="match in matches track by $index" ng-class="{active: isActive($index) }" ng-mouseenter="selectActive($index)" ng-click="selectMatch($index)" role="option" id="{{::match.id}}">
         <div typeahead-match index="$index" match="match" query="query" template-url="templateUrl"></div>
     </li>
 </ul>