rpc: revisit block and other RPC endpoints

[liamsi]

Tendermint provides a bunch of rpc endpoints which are partly used in the SDK too. They are also used by block explorers. We should revisit each endpoint from the lense of LL and need to modify or maybe even ditch some.

Particularly the Block endpoint (ref: #189) should probably just return the state transitioning Tx and not the whole Block.Data.

Nodes should request the Block.Data from ipfs / the p2p network like everyone else. To make it as easy as possible for block explorers and other existing tooling in the Tendermint/Cosmos ecosystem to also become LazyLedger block explorers, it would still be good to keep an rpc endpoint, that serves the Block minus the application specific blobs (messages). If that endpoint is still called Block and only serves the state-modifying portion, block explorers could easily switch.

ref: #189

Some examples of block explorers:
https://cosmos.bigdipper.live/blocks/5434576
https://www.mintscan.io/cosmos/blocks

[liamsi]

closing this for now. If anything we now want to extend the RPC and not limit it.