Improve "latest" version handling in publishing process

[wperron]

related to: #195 (comment)

Right now the "latest" version of a module is set to whatever the version number was on the last run of the async/publish function. This means that redelivering a failed webhook for a previous version could overwrite the "latest" version with a tag number that is older. I think we could improve the schema of the meta/versions.json object to include commit hash and commit timestamps so that the website can sort the versions by different parameters and give a better representation of a module's history.