workflows: task result templates

Adds templated task results for use in Holding Pen.

Before:
![Image]
(https://www.dropbox.com/s/0sryglpxpesfnh9/Selection_002.png?dl=1)
After:
![Image]
(https://www.dropbox.com/s/pfgo4fl8kltgv78/Selection_001.png?dl=1)

Also adds better documentation and other fixes.
I don't understand why we are serving the file here? Does it mean that any logged user can get any file?

Maybe you want to send file only from specific directory http://flask.pocoo.org/docs/0.10/api/#flask.send_from_directory .