requires react/addons when needed

In the future it would be better to have an utils/ directory with only classSet.

Fixes #5

Author: chollier

src/DateTimePicker.jsx

@@ -1,6 +1,6 @@
 var DateTimePicker, DateTimePickerDate, DateTimePickerTime, Glyphicon, React;
 
-React = require('react');
+React = require('react/addons');
 
 DateTimePickerDate = require('./DateTimePickerDate');
 

src/DateTimePickerDays.jsx

@@ -1,6 +1,6 @@
 var DateTimePickerDays, React, moment;
 
-React = require('react');
+React = require('react/addons');
 
 moment = require('moment');
 

src/DateTimePickerMonths.jsx

@@ -1,6 +1,6 @@
 var DateTimePickerMonths, React, moment;
 
-React = require('react');
+React = require('react/addons');
 
 moment = require('moment');
 

src/DateTimePickerYears.jsx

@@ -1,6 +1,6 @@
 var DateTimePickerYears, React;
 
-React = require('react');
+React = require('react/addons');
 
 DateTimePickerYears = React.createClass({
   propTypes: {