This reverts merge request !166

This reverts commit b3fb1a16

It introduced changes which cause issues described in
purescript-gargantext#571

This reverts commit a444cb30.

This reverts commit 22b14f56.

This reverts commit d04cf03b, reversing
changes made to e213a4bf.

It's not fully wired in, `convertQuery` for Arxiv is implemented as
`undefined`.

This commit simplifies the `ExternalAPIs` type, which is now a pure
enumeration, moving the lookup of the Pubmed key at the usage sites.
This simplified the code quite a bit, and made some otherwise-effectful
functions pure.

This reverts commit b7e406b1.

This doesn't block the whole view for the (long) period of refreshing
it.

This is safer than type Limit = Int

This big commit improves the jobs API in a way that now we can
completely abstract away over a JobLog.