Async Refactor: providers

[kumavis]

providers.js hasn't been touched in a while, so this is mostly directly taken from #82

Added some async/callback wrappers here and there and used pull-stream-to-async-iterator around datastore.query as #82 originally relied on the new datastore interface

Fixes #124

[dirkmc]

I suggested a couple of small changes. Is there a reason for adding async to methods that already return Promises? If I understand correctly this will just add an extra layer of Promises without any functional change in the code?

[kumavis]

@dirkmc committed the comment changes
The other points of feedback refer intentional to decisions I made, and I responded to the first instance of each

[vasco-santos]

This looks good @kumavis thanks!

Just two minor requests

[vasco-santos]

Also, could you increase the bundlesize max size in .aegir, in order to have a green CI?

[kumavis]

@vasco-santos @jacobheun ready to go

[vasco-santos]

LGTM! 🚀