Added support to filter on OS.
Progress on hb-10 Implement pivot table in LINQ.
Added Pivot() to LinqExtensions.cs.
Refactored HomeController.Bugreports() to use Pivot() for a lot less code to achieve the same.
Simplified BugreportsForDateVm.cs to mostly contain GoogleData property. Updated views accordingly.
Fixed hb-4 Create generic view for bugreport count over time

Via URL params:
Can choose between several properties on bugreport as X-axis or as data set grouping.
Can choose between line and column charts.
Can choose what to sort by and what order.