apply a special bg-color class to the body element when the Dashboard component is on screen to work around some flexbox, chrome, css shenanigans.  sigh.

fixes #1855 - prevents broken links in the activity feed for entries regarding the addition/removal of cards on dashboards.

update api endpoint GET /api/dashboard/:id to remove the superfluous wrapper with {:dashboard {real thing we want}}

move api endpoint POST /api/dashboard/:id/reposition -> PUT /api/dashboard/:id/cards so it's more consistent with the other dashcard api endpoints.

switch serialized cards over to hashes instead of url path elements.  this addresses the issue with long SQL queries generating large referer headers that cause Jetty issues.