p2p vendor code

[prestonvanloon]

Do NOT merge without #222.

The idea here is that we review #222 then merge it into this branch. Then we merge this branch into master.

This code doesn't need much review besides https://github.com/prysmaticlabs/geth-sharding/blob/p2p-vendor/vendor/vendor.json

[prestonvanloon]

Travis failing because

fatal: No url found for submodule path 'vendor/github.com/libp2p/go-floodsub' in .gitmodules
The command "eval git submodule update --init --recursive " failed. Retrying, 2 of 3.
fatal: No url found for submodule path 'vendor/github.com/libp2p/go-floodsub' in .gitmodules
The command "eval git submodule update --init --recursive " failed. Retrying, 3 of 3.
fatal: No url found for submodule path 'vendor/github.com/libp2p/go-floodsub' in .gitmodules
The command "eval git submodule update --init --recursive " failed 3 times.
The command "git submodule update --init --recursive" failed and exited with 128 during .

I wonder if this is due to me trying to use the (unmerged) gossipsub branch.
If that is the case, we may be blocked until libp2p/go-libp2p-pubsub#67 is merged

[prestonvanloon]

This is no longer needed with bazel