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.
* This technique is used in 3 places -- the generic plugin container (titlebar/body), the layer selector plugin (searchbox/body), and the draw/report plugin (tabs/body).

Note:
* CSS for TNC's other plugins will need to be modified as well.
* Also I expect that the UCSC "infographic" feature (for which we currently have no tests) will need to be modified

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.
* The panel jumps on dojo move unless the outer div has style="position: absolute"
Merge pull request #179 from RickMohr/resize-plugin-panels

Allow moving and resizing plugin panels