The notification component should transmit object names in a more readable way

[nilmerg]

Right now only host names are readable, service names however follow the <host>!<service> notation. Additionally, both do not use the display_name but the name.

Since Icinga Notifications Web will soon display the object.name prominently to the user, the component should use the following notation:

<host.display_name>[: <service.display_name>]