Standardize task arguments

[dcramer]

Task IDs:
app-name/env-name#task_id
i.e. getsentry/production#1

App versions:
app-name:version
i.e. getsentry:master or getsentry:a30331

This would make a lot of things more usable, and it's still very human readable. For example, in freight-cli:

freight tail getsentry/production#1

We could also default the environment like we do elsewhere:

freight tail getsentry#1

This should be clearly documented so its obvious that all features should be built with this in mind, especially the API (and it's responses).