Rename `current` release descriptor to `latest`?

[bertfrees]

The reason Javi added "current" was because:

Apparently latest has some kind of special meaning for github pages, and will not allow accessing resources that name, thus the current key word.

However accessing https://daisy.github.io/pipeline-assembly/releases/latest seems to work fine. Anyway, either "latest" or "current" should be removed to avoid confusion.

To do:

• Change default version in pipeline-updater
• Change value of "version" argument passed to the updater by updater-wrapper
• Rename files on http://daisy.github.io/pipeline-assembly (temporarily) and test
  • or possibly we can create an automatic test for this using a mock service (Docker?)
• Undo renaming of files until release has been made with new updater/updater-wrapper

[rdeltour]

I removed the latest descriptor, which wasn't used. Both @bertfrees and I agree that latest is more explicit than current though, so we should consider whether renaming is easy (the keyword is hardcoded in the descriptor, so the updater would need to be updated itself).