Deprecate QuickStatements mode

QuickStatements mode predates OAuth, but these days OAuth is the primary
mode to use the tool in (without OAuth, you can’t define new depicts
statements, add regions for somevalue/novalue, or edit existing
regions). Supporting QuickStatements mode makes the JavaScript code a
lot more complicated (I noticed this while adding editing support), so
I’d like to remove it if (as I suspect) nobody uses it.