Export and print for Views and widgets

[engram-design]

Let clients export Metrix data and Views for reporting: CSV for tables, image/PDF for charts and full Views, plus a print-friendly layout.

1. CSV export for Table (and Counter summary) widgets.
2. Chart image export (PNG) for Line/Bar/Pie.
3. Print stylesheet for a View.
4. PDF export of a View (server or client-generated) with title, date range, and widget snapshots.