emit original quill event information with 'change'

[mgmeiner]

With this PR i want to provide the original event parameters of the 'text-change'-event from quill to listeners of the 'change' event of the vue-quill-editor wrapper. I also changed the parameter naming from 'oldDelta' to 'oldContents' to match the current quill event documentation)

This change is 100% backward compatible. I also updated the examples in which a listener on 'change' is registered

Background info: In some cases i need to get the delta from a change and the source of the change. Currently i register an additional listener directly on quill but with this PR this would get much easier.