Use Ember.TextField instead of generic Ember.Component

Datepicker is an input field, so it much better to use Ember.TextField.
It automatically gives attributes like `name`, `size`, `placeholder` and etc.

This also closes #2

Author: soulim

addon/components/bootstrap-datepicker.js

@@ -1,8 +1,6 @@
 import Ember from 'ember';
 
-export default Ember.Component.extend({
-  tagName: 'input',
-
+export default Ember.TextField.extend({
   setupBootstrapDatepicker: function() {
     var self = this,
         element = this.$(),