Messages modal cornverted to Bootstrap

#### Move modals from mootools to Bootstrap
NOW this IS the last PR to get all back end using bootstrap modals. The rest are: #4513 #4514 #4561 and #4562 

Testing:

Try the my settings button on Components->Messaging

------
On administrator/index.php?option=com_messages the settings button on the toolbar uses modal

![screenshot 2014-10-12 09 07 49](https://cloud.githubusercontent.com/assets/3889375/4605258/7ef8c596-51d6-11e4-921c-445687d7a165.png)
![screenshot 2014-10-12 09 08 03](https://cloud.githubusercontent.com/assets/3889375/4605259/8146172c-51d6-11e4-889d-e650feb042f2.png)

You can replace all this with:

```php
echo $this->form->getField('lock')->getControlGroup();
```

It will take care of adding the `control-group` structure for fields. You save lines and our markup can be changed / overriden in 1 single function.