camelCase all the config options

camelCase goes better with the code. @rfk r?

@gene1wood only the names have changed, values remain the same. Here's the mapping of changes:

```
bind_to -> listen
domain -> (deleted)
srp -> (deleted)
public_url -> publicUrl
smtp.verification_url -> smtp.verificationUrl
smtp.report_url -> smtp.reportUrl
smtp.template_path -> smtp.templatePath
toobusy.max_lag -> toobusy.maxLag
mysql.create_schema -> mysql.createSchema
l18n.default_lang -> l18n.defaultLang
l18n.supported_languages -> l18n.supportedLanguages
l18n.translation_directory -> l18n.translationDirectory
l18n.translation_type -> l18n.translationType
```