Fix EZP-22092: Update TinyMCE to 3.5.10

JIRA: https://jira.ez.no/browse/EZP-22092 actually to fix https://jira.ez.no/browse/EZP-22024

# Description

In Chrome, the custom tags are removed by TinyMCE when, for instance, the editor removes an empty line. This is due to [this TinyMCE bug](http://www.tinymce.com/develop/bugtracker_view.php?id=5641) which is fixed in TinyMCE 3.5.9. So this patch updates TinyMCE to the last 3.x version to get this fix.

# Tests

manual tests in Firefox, Chrome and IE9