Stillage layout

[tfrayner]

Positioning of casks on the stillage can be stored in the database, but we
currently have no good way to edit this. Two components are required:

1. A means, preferably graphical drag-and-drop, to move casks into
   position;

2. An automated procedure for placing casks into a "best-guess" location
   prior to manual editing.

   It is entirely possible that these requirements may be fulfilled in a
   separate component, i.e. not using the web interface.