Support for Grafana 5.0 folders

[marckhouzam]

Grafana v5 introduces the notion of folders in which we can group dashboards. http://docs.grafana.org/guides/whats-new-in-v5/#dashboard-folders

A quick test with wizzy 0.6.0 to import dashboards and export them back shows that the folder structure is not preserved.

It would be nice to add this feature to wizzy.

[quadriq]

see my PR https://github.com/utkarshcmu/wizzy/pull/125