Replace existing runtime code with new runtime

[rphmeier]

Meta/Tracking issue + final wiring instructions.

Depends on

• Write a registrar module #1508
• Parachain/thread swapping #1509
• Add an origin for Parachains #1510
• Create a parathread auction module for collators to bid on parathread slots #1512
• Integrate slots module with paras and new registrar #1513

to reach approximate feature parity with the old.

We'll want to add all of the modules, alongside the initializer, to the construct_runtime macros.

Furthermore, we need to wire up Initializer as a OneSessionHandler, and, more importantly ensure that Babe is always called as a session handler before the Initializer. This is because Babe only computes its new randomness value in its session handler implementation, and we need to use the new randomness for validator group assignments, not the old one.

[rphmeier]

Closed; everything except for parathread stuff is done and we will revisit that later.