Allow moving and resizing plugin panels

Use dojo Moveable and ResizeHandle
* Pass paneNumber down to plugin so it can make a unique ID

Adjust CSS so plugin panels respond gracefully to resize
* Main area of all plugin panels must have "height: 100%"
* When there's a header above the main area, use trick of setting parent div's "padding-bottom" to height of header, so the 100% height won't include it.

Also:
* The dojo resizing "ghost box" gets drawn in the wrong place if the target div has padding/margins, so add an extra plugin-container-outer div that has none.