Show a buble containing the result of the called commands
Make daemon commands configurable

Now each daemon can have different available commands.
Sample configuration and config guide in the README.md are updated.
Create Service class and refactor Daemon class to inherit from it

Service class is needed as an abstract class to avoid code duplication
when extending the application with non-deamon services.
Add VirtualBox support

With this feature the configured virtual machines could be managed
like the daemons. Every virtual machine will have it's own menu item
with a submenu to provide basic commands for the machine.