High-level Architecture diagrams

[liamsi]

We should add architecture diagrams that clarifies at least the following relations:

1. LazyLedger layer-1 (including block producers/validators)
2. application specific sidechain dealing with state (and maybe block producers of that chain)
3. end-user client submitting Tx

The first version of this can be a very simple draft. Point 3) could also be skipped in a first diagram if that simplifies things. Additionally, more detailed diagrams explaining all touching points and interactions between all three would be great.

[liamsi]

I think this is still useful but these diagrams are not necessary to live in the specs repository but for developer focused documentation. Let's aim for testnet and incentivized testnet the latest.