Incorrect result when image is quoted

[Reinmar]

The image should not be quotable now due to https://github.com/ckeditor/ckeditor5-image/issues/54. And after iteration 9 it wasn't – it was always skipped by the quote command. Right now, on current master branches I get this:

[Reinmar]

Bad commit according to bisect:

(detached:bisect/bad~1 cb2feef ?1) p@m /workspace/ckeditor5> git bisect good
ab5b5494e5eba7beb4a3bac4ea9c5e6d59a610f5 is the first bad commit
commit ab5b5494e5eba7beb4a3bac4ea9c5e6d59a610f5
Author: Travis CI User <travis@example.org>
Date:   Tue Apr 11 16:45:47 2017 +0000

    Revision: https://github.com/ckeditor/ckeditor5-image/commit/02869eb4478a2f538006c128b30b9727617af665

:100644 100644 611526d5c4beae7046b0a08ec36843cbbe642175 35acdd8ba971d8127dd462a9c8c1162a54f00d58 M	mgit.json

So, it's this ticket: https://github.com/ckeditor/ckeditor5-image/issues/94.

[Reinmar]

As I explained in https://github.com/ckeditor/ckeditor5-engine/issues/532#issuecomment-299204504 this is a result of Schema's poor behaviour. The schema for image and caption is now totally incorrect, so, as a result, caption is a block element and blocks are allowed in blockQuote...

Fortunately, blockQuote is not yet allowed in image (and won't be, even after https://github.com/ckeditor/ckeditor5-image/issues/54) and apparently we miss a check whether blockQuote can be applied at that level.

OTOH... AFAIR the entire implementation of the block quote command bases on the assumption that blocks returned by Selection#getSelectedBlocks() are children of the same element ;| Which would be true for now if not this case. It may, therefore, require more thinking.