Get N most recently modified workflow instances through REST API

[eputtone]

We've had this idea/request for showing something useful immediately when you land on Explorer:

Workflow instances should maybe show something initially instead of a blank page? E.g. the most recently modified workflows, to make it quicker to access those.

I'd be happy to implement it to nflow-explorer-ng, but the REST API does not support sorting by any field. There could be sorting for other workflow instance field as well.