Very basic implementation of interactive mode
Introduce 'exec' route; refactor
Merge branch 'master' into 75-interactive
Merge branch 'master' into 75-interactive
Updated interactive mode.

Doesn’t play nicely with the html operator yet.
Add a loading spinner in interactive mode
Interactive now works for html output
Move class to body element
Merge pull request #99 from okfn/75-interactive

[#87]: working interactive mode - #87.