Use uvloop instead of asyncio

[johanhenriksson]

Investigate potential benefits of replacing the default asyncio event loop with uvloop

[OskarHandmark]

For creating tasks within Cowait this probably isn't noticeable compared to the overhead of actually creating the containers. Since we use asyncio for pretty much everything (websocket communication between tasks, async RPC calls and whatever user defined async operations are executed within tasks (ie scraping or other high IO operations), I think this is a good idea.

• uvloop only works with asyncio. It cannot work with Tornado, gevent, curio or similar.
• uvloop requires Python 3.7.
• If we decide to use uvloop, we could still have python 3.6 support by simply not installing uvloop. If you're using Python 3.7 or greater, we can add the library and "install" the event loop using uvloop.install() or asyncio.set_event_loop_policy(uvloop.EventLoopPolicy()).

A good performance test (that applies to Cowait) is just to benchmark a few tasks that spams lots of logs.