[423] Handle many more graphing edge-cases.

Prepare graphs for an expected time period (since July 2012) rather than for the time period found in the DB, which can be reduced to absurdity with certain queries. Graphs always have a consistent X-axis, ugly logic to combine disparate data series can be removed.

On 'Publisher' and 'Dataset' tabs, always graph the *top 20* series regardless of the month currently rendered in the table. This makes more sense from a useability POV.

Finally, some client side error checking was improved.