Cht-core: Remove empty parents migration scalability

[garethbowen]

The remove-empty-parents db migration attempts to download all contacts including docs and then process them one by one. On a large data set I expect this will crash.

Do some sort of batching instead (limit and skip), and use bulk docs to do the insertion.

[garethbowen]

Assigning to @alxndrsn because I _think_ I saw him talk about this issue on Slack...

[alxndrsn]

Now using a temp view, similar to migrations/convert-bad-dob-format.js.

[alxndrsn]

No limit or skip, and no bulk update, but should now only be getting a few docs per project, instead of _ALL_ the contacts.

[garethbowen]

Commit: https://github.com/medic/medic-api/commit/bf254319e1be187b1587455ba5912019da6852b5

[garethbowen]

Original issue: #2436

[garethbowen]

One comment in the commit. Also there are a few jshint errors to fix.

[garethbowen]

I've fixed jshint to unblock master.

[garethbowen]

No AT required.