Fixing workpackage-ajax-update (#1823, #1422)

The ajax-update-functionality for workpackages wasn't properly wired:
Due to the renaming, some dom-references pointed into nowhere; the
second bug (wiki-toolbar not properly initialised) was also caused by
wrong/changed dom-references.

 * wired the listener to the edit-button
 * added the js-response to the work_packages_controller
 * dom-references fixed for wiki-toolbar-initializers