registry dapp: cleanup, support reverse entries (#3933)

* style fixes ✨

* registry dapp: show reverse events

* registry dapp: actions & reducers for isTestnet

* registry dapp: make Hash & Address components

* registry dapp: code style ✨

* registry dapp: bugfixes 🐛

* registry dapp: postTx helper

* registry dapp: refactor reducers

* registry dapp: use react-redux

* registry dapp: actions & reducers for reverse lookup

* registry dapp: reverse lookup component

* registry dapp: connect Address to redux

* registry dapp: de-DRY recordTypeSelect

In preparation for the next commit.

* registry dapp: support reverse lookup

* registry dapp: render reverse events

* registry dapp: show tx sender, add key prop

* registry dapp: link accounts to etherscan as well

* registry dapp: address style grumbles 💄

* registry dapp: address style grumbles 💄