Fixes for Polkadot Integration (#586)

* Add AccountIdConverter impl to Kusama and Polkadot primitives

* Add missing message lane config constants

* Add more consts

* Add another missing const

* Move consts in primitives so that they're consistent across files

* Move types and consts to more intuitive locations

* Downgrade hyper from v0.13.8 to v0.13.6

This conflicts with a requirement on the Polkadot side
which requires that hyper is =v0.13.6

* Update hyper to v0.13.9

* Update async-io to v1.3.1

* Update socket2 from v0.3.15 to v0.3.18

* Update message weight/size constants

* Make BlockWeights/Length parameter types

Allows us to re-use these types from both the runtime and
the message lane config files without creating a new instance
of them.

* Remove uneccesary weight constants

These can be found in the `runtime-common` crate used
by Polkadot/Kusama. The constants there will also be
the most up-to-date versions.