Changelog A.E.: Update 6

Database.cs

- CreateBranch() added and tested
- RemoveBranch() added and tested
- connection.close after each database access
- comments and formatting

CarsharingSystem.cs
- comments
- bool dataChanged added
- property bool DataChanged added wich reloads the DataSet and the lists
from the Database if its getting changed to "true"
- DataChanged = true on every method wich is writing the Database
- added regions vor better code overview