Call into Keplr Extension via OfflineSigner interface

Depends on #264

A web dApp should be able to use this same Wallet interface that it uses to access local key material stored in the browser, to send a signing request to the Keplr extension. Ideally work with @thunnini to get the client code working. This has two steps:

• Submit a simple x/bank SendMsg to the Keplr extension to be properly signed
• Add support for x/wasm CosmWasm 0.9 messages to Keplr and sign them with the extension (requires many changes to Keplr)

Bonus:

• Figure out how to test such integration in CI - node/webapp calling extension that posts tx to local blockchain in CI.

[willclarktech]

See

• https://github.com/chainapsis/keplr-extension/pull/21
• https://github.com/chainapsis/keplr-example/pull/3

[ethanfrey]

I was thinking about how to demo this and do we need to build a minimal wallet as a frontend app to show integration.

Then I came across https://github.com/chainapsis/keplr-example/blob/master/src/main.js which is used to demo calling the extension from a webapp using cosmosjs. We can port this code over to use cosmjs and provide this as a proof of concept that the integration works