This paves the way to a more effective search in corpus by modifying the
internal "leaves" type of the `Query` type from a `Term` to a new type
called `QueryTerm`, which can either be an extact match or a partial
match, which can be rendered into a proper Postgres TS query via the
":*" syntax.

This reverts merge request !166

This reverts commit b3fb1a16

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

This commit adds a bunch of Arxiv tests to demonstrate we can
successfully transform our `Query` type into the Arxiv AST.

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