BK-2367 Add ability to select layouts for images

[ride90]

Hi @eos87 ,
Finally this fat PR is here.
It still has some issues, I guess user will not experience them in 99 percents of cases :)
I hide images from "contentrevision" for now, because we are not displaying images in diff correctly.
Image layouts feature for now supported only by epub 2/3 and xhtml outputs.
It also supports pdfreactor output, you can find update for css in pdfreactor repo (only one theme), other themes will be updated by @MiczFlor with generator.

[eos87]

Hi @ride90, it looks pretty good, although I found small issue.

To reproduce:

1. Add an image
2. Edit Layouts (play with different options and close modal saying you need more than one image)
3. Click Remove
4. You will see the error

I saw another which was a modal warning saying about full page image, but I was unable to reproduce it, after seeing that modal I was not able to do any other change. I'll keep trying and If I find something I'll let you know.

Other than that, it looks really good! great work my friend :)

[ride90]

HI @eos87 , yes, I was able to reproduce this issue.
It is not connected with image layout feature (it feels like it is actually). I will provide fix in separate pr.
Thank you for a review.