Integrate Monix into all submodules

[fwbrasil]

Currently, only the Cassandra module has integration with Monix. I'm not sure that all drivers have APIs to implement proper streaming though.

[lvicentesanchez]

Slick 3.0 doesn't use asynchronous drivers for the streaming part, but they have a dedicated execution context that they handle for the user. We could do the same for non-streaming-friendly modules like the jdbc one, use a dedicated Scheduler properly configured.

[fwbrasil]

Monix now depends on cats. I'm closing this since I don't think the integration is worth the additional dependency.

[deusaquilus]

If Monix is out, what about Akka?

[deusaquilus]

@lvicentesanchez, it's worth noting that Slick has been plagued by transactional deadlock issues starting at version 3.0 where they moved to reactive streams. See slick/slick#1274, and slick/slick#1614. I don't think it's completely clear yet that even with a scheduler using a strict connection-per-thread policy this problem is completely solved. Maybe the simpler way of reasoning that was in Slick 2 is a more reliable way to go. At least when using JDBC.