Move some skin styling from ve.ce.Node.css to a shared skin css file

The styling of the image thumbnails should be controlled at the
skin level, not by the generic VE styles. Moving the thumb/figure
styles from ve.ce.Node.css to ViewPageTarget-shared.css. Otherwise
no changes to the styles themselves.

Also adding minerva (the mobile skin) to the list of supported skins.

Bug: 60542
Change-Id: I67ab6d5b91cee7e587f61df26e7dae74c1068788
Merge "Move some skin styling from ve.ce.Node.css to a shared skin css file"