Stuck on "Logging in"

**Describe the bug**

HyperDEX gets stuck when logging in. It only happens sometimes. I've managed to narrow it down to the `enableCurrencies()` call in `api.js`. Sometimes a call there gets stuck, which blocks the login. And it only happens when the app is built, not in development.

I could consistently reproduce the issue earlier today with these currencies:

```json
[
"BCH",
"DNR",
"DOGE",
"EQLI",
"LTC",
"MSHARK",
"VTC",
"ZEC"
]
```

But after lunch it started working again... With the exact same version and config.

When I was able to reproduce it I could consistently get it working again by limiting the currencies to less than 6, but not always.

This feels like marketmaker choking on Electrum calls somehow and not correctly timing out.

What I've tried:

- Upgrading/downgrading Electron.
- Upgrading/downgrading Marketmaker.
- Making the `enableCurrencies` call serial instead of concurrent. It should already be serial internally though, because of our queueing.
- Lots of other things I've forgotten now.

I'm running out of ideas now. It seems very random and I could even reproduce it on older HyperDEX versions.

I could try adding a custom Electrum timeout like explored in https://github.com/atomiclabs/hyperdex/pull/343/commits/7284aa75df1e01d1813774392944615db76ee6cf

**System info**

- OS & version: macOS 10.14
- HyperDEX version: `master`, 0.2.1, 0.2.0, 0.1.4