Add protocol explorer

@jozanza made some really nice documentation about build the protocol explorer - https://github.com/livepeer/livepeerjs/tree/master/@livepeer/explorer

We should add this into the devenv as part of the contract deployment process.

Start by reading the protocol explorer documentation at https://github.com/livepeer/livepeerjs/tree/master/@livepeer/explorer and locating devenv's contract deployment entry point. Confirm what the local test environment currently deploys and define done as having the explorer included in that deployment process.

Written by the indexing model from the issue text.