Change properties to conf (HOCON) files #30
Description
Replace the properties files that hold the messages with conf files in HOCON syntax.
Also, replace Java's ResourceBundle with PureConfig https://github.com/pureconfig/pureconfig.
The messages could be read as Map[MessageSource#Key, String] or we can define a proper case class for it, dunno... it would be great to use the MessageSources and Keys themselves to get the messages instead of mapping them to Strings.
It is related to #3, so don't forget the localization.