Add lock files to Hercules

[paulf81]

This is a maybe item, but we discussed adding lock files to Hercules to enable exact repeatability of workflows

[paulf81]

Googling around I'm not positive if this is a good idea, it could be though. The main notions I have is:

1. Committing a lock-file is appropriate if the repo is the end thing (an app)
2. It's less appropriate if the repo is something to be imported (a library)

Hercules is more (1) than (2) I think so could still be good but worth considering