Create ui subpackage for Notifications

This package contains all user interface components to use and configure
Notifications.
Add SoundPanel

This is a JPanel that allows the customization of a Sound Notification.
It supports build-in and external sounds as well as setting the loop
mode.
Add MessagePanel

This is a JPanel that allows the customization of a Message
Notification. It allows the user to configure the title and the content
of the message.
Add NotificationConfigurationDialog

This is a Dialog which allows the user to configure a Notification. It
contains a SoundPanel and a MessagePanel. It allows the user to test
their Notification using a NotificationButton. If both Sound and Message
are selected the Dialog will create a CombinedNotification.