Apply TinyMCE security fix for CVE-2012-6112

Apply TinyMCE security fix for CVE-2012-6112 from
https://github.com/tinymce/tinymce_spellchecker_php/commit/22910187bfb9edae90c26e10100d8145b505b974.
Added the meta generator tag to the back end templates
Merge pull request #5288 from taca/tinymce-CVE-2012-6112/3.0.4
Correctly determin the last run of the command scheduler (see #5278)