MDL-76734 editor_tiny: Listen to TinyMCE submit events

jQuery submit events do not trigger the native submit event, and
therefore the TinyMCE submit listener is not called. This means that the
tinymce.triggerSave() function is not called, and the editor content is
not saved.

To work around this, if there is a form for the Node that the editor is
attached to, the jQuery submit event is listened to and the save event
called.

Unfortunately it is not possible to use a global jQuery submit listener
added to the document to save all editors on the page.
In some cases, this is too late because the bubbling process means that
a child node consumer may attempt to consume the data before the
delegated handler is called for the document.