Implemented SMTP emailing

Adds the ability to use Email exports in XML definitions.

*Sample EmailExport definition in `services/`*
```xml
<exports>
    <email name="gmail" to="recipient@gmail.com" from="sender@gmail.com" subject="Demo Report" />
</exports>
```

*Sample Email settings configuration in `conf/email/`*
```xml
<emails>
    <config
        name="gmail"
        host="smtp.gmail.com"
        user="someone@gmail.com"
        pass="password123"
        port="465" />
</emails>
```