Move content history to bs modal

Same as #4513 and #4514 but for content history

Content history is currently using mootools modal.
Without affecting in anyway the logic of the field we can use jQuery and bootstrap.

B/C
Should be 100% compatible

Test:
Apply the patch
Go to administrator -> Banners -> create a new banner
change the alternative text and save it again
repeat the last part for few more times

press the versions button
Everything should be ok

Before:
![screenshot 2014-10-12 03 17 54](https://cloud.githubusercontent.com/assets/3889375/4604532/5148c820-51a5-11e4-947b-f1bd0ea00a86.png)

After:
![screenshot 2014-10-12 03 17 04](https://cloud.githubusercontent.com/assets/3889375/4604533/5eceaaf0-51a5-11e4-9000-e019843c1a96.png)

You don't need that. Just use the constant `JPATH_BASE` which already does exactly that. Or pass `null`, because the default value for the argument is `JPATH_BASE` :smile: