Handle legacy html entities

For EPUB 3, the content should be html5 compliant xhtml. This means
you can only use amp, lt, gt, quot and apos entities, unless you declare
the dtd in the doctype. This change attempts to parse legacy xhtml and change
it to more compliant html.
Don't update model on a blur event.

Aloha always raises a smart-content-change event with a triggerType of 'blur'
when the editor loses focus. This causes models that haven't been changed
to change the moment you click outside the editor. By ignoring blur events,
the model will only be marked dirty if you actually change anything.