The module only contained one function actually used, `leftJoin3'`, so I
I redefined it inline where it was used, and removed the module.

Since Weeder can't deal with TH, we make a guess about what symbols TH
depends on, based on whether they contain underscores and whether they're
in a module named `TH`

Also, we're now properly using using regular expressions.

This pattern was actually only here for `gargantext-settings.toml`, but
other `.toml` files should not be ignored by default

Also started adding some stuff to `weeder.toml`, but it should be
discussed some more.

Resolve "Fix test build warnings"

See merge request !376

Also, add -Werror to tests so that no warnings in tests are reported anymore.

Switch to OpenAPI3 from Swagger2, to use proper Bearer token

Closes #427

See merge request !369

This commit adds three major tags to the swagger UI:

* Gargantext (like before): this spells out all the endpoints;
* Private operations: lists private backend ops;
* Public  operations: lists public backend ops.

More can be added, but the machinery used here should serve as a
blueprint.

OpenAPI3 will allow us to properly pass the Bearer Auth to the servant
swagger UI.

I fixed those warnings that were easy to fix: redundant imports, unused
variables, etc. (I might have missed some though)

The warnings I deliberately left for now are:
* In `Test.API.UpdateList`: Incomplete pattern matching (we would need
  to think a bit about error handling to fix this)
* In `Test.Utils`: `traceShowId` remains in code (we would need to think
  a bit about proper logging to fix this)

Resolve "Refactor `Gargantext.Database.Prelude`"

Closes #421

See merge request !372

Those definitions felt very ad hoc, and were not used a lot in the
codebase, so I simply replaced them with their definition.