Config email by type of advice

Allow configuration for type of advice to be emailed.  Any combination of 'BUY', 'SELL', or 'HOLD'.

```config.mail = {
  enabled: true,
  sendMailOnStart: true,
  what: ['BUY', 'SELL', 'HOLD'],  // email all advice
  email: 'my@email.com',
 password: 'password'
}
```

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