Backport Messages modal converted to bootstrap

[zero-24]

see: https://github.com/joomla-extensions/messages/pull/7 and #4563 we initial move that code to the messages repo but is should be also in the main repo.

All the work is done by @dgt41 and this change is allready tested see: http://issues.joomla.org/tracker/joomla-cms/4563

(Restored initial PR comment on #4563)

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Move modals from mootools to Bootstrap

Testing:
NOW this IS the last PR to get all back end using bootstrap modals. The rest are: #4513 #4514 #4561 and #4562

Try the my settings button on Components->Messaging
On administrator/index.php?option=com_messages the settings button on the toolbar uses modal

[zero-24]

Woops wrong base branch. I will reopen it later.

[dgrammatiko]

@zero-24 can you redo this one, it's still valid and probably needed 😉

[zero-24]

Did i never redon it? I hope i get time this week.