Adds body-width to image selectable styles.
Fixes a bug where whitespace in pasted text would disappear.
Displays source below video blocks.
Extends source information to most other blocks.
Merge branch 'feature/source-below-blocks'
Adds support for visual drop-targets.

Those are now visible when dragging. It needed some scrolling around to
ensure the current block remains where it is relative to the current
viewport.
Merge branch 'feature/highlighted-droptargets'