Add text download to framework app

Plugins can now use ``app.downloadAsCsv`` and
``app.DownloadAsPlainText`` to download textual data.
Draw&Report plugin to export CSV

This plugin has been updated to use the new text downloading
functionality of the framework as an example.  The front end
reports are converted to a denormalized, structure json document
that is downloaded as a valid CSV
Merge pull request #284 from mmcfarland/topic/client-side-csv

Enable client side CSV export