spec: Light Client Supervisor

[josef-widder]

This is the first draft (rendered) for the lightclient supervisor. It addresses (partly)

• the new lightstore semantics Lightstore Invariants + Maintain Verification Information #499,
• the proposed changes to the parameter handling from spec: Rust like pseudo code for Sequential supervisor and core verification #509,
• initialization from Genesis Use the Genesis state as a Trusted State in the light client tendermint/spec#131

In the spec, we call a function AttackDetector which will eventually implement the latest ideas to compute evidence to address #461 (although proof of fork will only survive for the IBC use case).

There are still many TODOs. I hope it is understandable nonetheless. I would prefer to start to work on the AttackDetector Spec now, before polishing this one.

[josef-widder]

Opened a PR at tendermint/spec#159 as we move all spec work to the tendermint/spec repo.