Toolbar support for visual cells

[tdudgeon]

As some of the visualisation cells become more capable it starts to be more important to give users direct access to changing cell settings. The advanced option panel is too clunky for this. A better solution is a toolbar at the top of the cell that can be used to change the settings.

This does not replace the need for the advanced settings panel as some things might still be more appropriate there, but some options would migrate to the toolbar.

It should be possible to show/hide the toolbar like it is possible to show/hide the cell description.

The most obvious need for this is in the 3DMol cell where several settings would be useful from a toolbar, but most of the other visualisation cells could also use this.