Attempt to fix docker sponge error
stbt batch report: Provide .json data to templates

Really css_class, etc. should be refactored to be jinja filters, if we want to
use server-side jinja templates at all in the long run.

Also need to resolve the issue of namespacing and overriding.
Fixup service: Allow different paths to tests-pristine between host and container
stbt-run: Tell the user why if it can't load git information