Replace co-generators with async-await

[art-in]

latest co (4.6.0) in nodejs (7.2) doesn't work with generators (for whatever reason)

"TypeError: You may only yield a function, promise, generator, array, or object, but the following object was passed: "[object Object]"

async-await works since 7.2 with --harmony flag, or in 8.0 (nightly) with no flag.

• [x] investigate nightly 8.0 (stable? all tdl cases works well?) RES: yep, but using 7.5 with --harmony flag
• [x] remove co() on server
• [ ] remove co() on client