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

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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)

Same here: no inline styles.