build ag-chain-cosmos tool

[warner]

Like ag-solo, we want an ag-chain-cosmos tool (maybe abbreviated agcc) to create, configure, and start a chain node. I'd like it to create a new base directory and copy the relevant files into it, including the various starting vats and bootstrap code for the demo. agcc is roughly a frontend for the cosmos-sdk's "baseapp" program, but putting the state in a specific base directory (rather than some $HOME/.dotsomething), and copying the swingset-specific files in addition to creating the normal tendermint ones.

The subcommands should probably be:

• agcc init BASEDIR: mkdir, copy files in, do the equivalent of the cosmos-sdk baseapp's init function (create a genesis.json, a validator keypair, etc)
• agcc add-genesis-account
• agcc tendermint
• agcc start

This tool might be pretty short: init needs to do extra work after delegating to the baseapp's version, then the other commands need to basically assert that CWD is a real basedir and then add --home . to whatever the command was. It also needs to do all the golang+node.js magic from the current lib/ag-chain-cosmos.

[warner]

in the old repo. this was cosmic-swingset issue 8