Add in support for data visualizations using the query string

If the `spreadsheet` property is set in the GET request query string, Because will load and render data from a Google Spreadsheet. Right now, it only takes the key (e.g. `0Ar2Io2uAtw9TdEFvb2t5U3BiZDhQRlNSRjRTY3Q2Rmc`).