Unify application notifications

[TiSiE]

Currently the various notifications the application displays on the site are very chaotic.
e.g. if a job application is saved, the notification is displayed underneath the headline, but if one logged out, the notification is displayed above the headline.
Internally (in the code), the notifications are handled different.
As view variable, as flash message (session based).

The goal is, to unify the notification management, to reduce code duplication and ease the development process.

The idea is to only use session based notifications based upon the ZF2 FlashMessenger. But to further enhance it by providing a new Controller-Plugin and View Helper Plugin, to simplify it even more.
Notifications will be rendered by attaching a child view model to the layout, to allow other modules to alter the way, the notifications are displayed.