The signature request e2e tests were previously using ropsten. This
expectation was even hard-coded into the test contract dapp.
Instead the contract-dapp has been updated to use the current `chainId`
when calling `signTypedData` (falling back to the `networkId` if
`chainId` is not set). The fixture used by `signature-request` has been
updated to use ganache.
* Add network store for testing
An alternative persistent state store has been created for use with e2e
tests. Instead of reading state from disk, it tries to load state from
a local fixture server running on port `12345` and serving state from
the path `/state.json`, and returns a blank state otherwise.
* Add e2e test fixture server
A fixture server has been added for serving background state, which the
background will read upon startup as part of restoring persisted state.
The `signature-request` e2e test has been updated to use a fixture to
bypass the registration step. The fixture used (`imported-account`) was
generated by pausing midway through that test run
