added guava dependencies
bind guava EventBus in session scope
created example login event
added example for posting a login event via guava EventBus
added example for handling a posted login event
Merge pull request #288 from davherrmann/issue#282

Issue#282
Nach erfolgreischem Login wird User in Properties bereitgestellt
added class containing a message and a message type for a notification
system via Guava EventBus
Merge pull request #298 from davvitt/issue#292-LoginUserBereitstellen

Nach erfolgreichem Login wird der User in Properties bereitgestellt
Rename columns in SchoolYear
Merge pull request #300 from jidel/issue#293-db

Rename columns in SchoolYear
example for posting a MessageEvent on an unsuccessful login attempt
added MessageEvent handler method in MainUI
 - shows a Vaadin Notification with the chosen style and message
Merge pull request #301 from davherrmann/issue#282

Issue#282
Merge remote-tracking branch 'upstream/develop' into issue#290