Unify the two configuration classes

[mpreisler]

The image-scanner and openscap-daemon projects merged together and due to time constraints we have made some compromises.

One of them is the existence of applicationconfiguration next to config.Configuration. The code should be refactored to only use the latter. The hard work of removing the singleton has already been done by @baude in #13. The next step is passing self.system.config in the dbus_daemon class instead of letting the cve_scanner.Worker construct the applicationconfiguration instance.

[mpreisler]

#93 will get rid of this.

[matejak]

This is a sortof duplicate of #93