Standardize runtimes

[JoshOrndorff]

This PR takes the opinion that a "standard" runtime should not be tied to any particular consensus-related APIs or pallets such as the babe_api or the aura_api. Existing nodes are converted to instant-seal. This allows pruning of the pow-runtime, and opens up the possibility of adding some interesting recipes in a natural way in the future. For example:

• Pure PoA - An aura-like consensus engine that live outside the runtime
• Babe/Grandpa node - A node/runtime pair where consensus authorities are dictated by a runtime API (like polkadot)

This PR includes:

• Update kitchen node to instant seal
• Update RPC node to instant seal
• Manual-seal node uses super-runtime (and other standardized runtimes)
• Standardize super-runtime
• Standardize ocw-runtime
• Standardize weight-fee runtime
• Standardize API-runtime
• Remove PoW runtime (it previously existed just because I needed something without
• Figure out how to make the light client actually build in the instant- and manual-seal nodes This is figued out and demonstrated in Manual seal light client #238 but needs an upstream PR. FIXME annotations are added to the code here.
• Write up babe-grandpa recipe (mention node template is similar with aura instead of babe) This is deferred to a followup Add writeup for babe grandpa node #239
• Write recipe for kitchen node
• Prune instant seal stuff from manual seal node. (We have lots of instant seal nodes now.)

[JoshOrndorff]

@andresilva I've written this PR after our riot conversation the other day. It converts the recipes' nodes to instant-seal as you suggested. I'm hoping you could:

• give it a quick general look tfor silly mistakes or oversights
• help me figure out why I can't get light clients to compile in the instant-seal nodes