Add browser testing

[moodysalem]

I'm submitting a ...
[ ] bug report
[x] feature request
[ ] question about the decisions made in the repository
[ ] question about how to use this project

Summary
This client needs browser testing - using any browser testing framework, validate that the client can be successfully packaged and ran in the browser. Because it uses isomorphic-ws and cross-fetch, it should be able to run in browser and node environments

[moodysalem]

One issue that might be encountered here is hapijs/joi is not built for the browser and has several node-only dependencies, so one of the steps might be to replace joi with joi-browser in the @ethercast/model dependency

[moodysalem]

@ethercast/model is no longer dependent on joi

[spm32]

Hey @moodysalem, saw a bounty request was put up on this issue, are you still interested in having us put some funds towards this one?