Fix legacy jQuery.ajax() success function being called when HTTP connection refused.

http://bugs.jquery.com/attachment/ticket/5968/0001-Fix-jQuery.ajax-success-function-being-called-when-H.patch
WIP: Add save button to Ace Editor to save source code while staying on the same page.

This has several benefits:

* No need to exit maximize/fullscreen modes to save.
* The cursor position in the editor does not change.

TODO:

* Not generic enough, mainly targetting ZODB Components for now.
* Comments.
* JSON for error message list.