Make it possible to opt-out of epi-image-editor and image plugin selectors in TinyMCE

Currently the TinyMCE plugins epi-image-editor and image activate (and highlights) for every img -tag in the editor.

As an addon developer it would be nice to be able opt out of this behavior, without having to disable the existing plugins, to allow using external or more specialized editors for img objects.

An example could be that any img tag with a specific attribute (for example data-disable-image-editors) would be ignored by the existing epi-image plugins.