Changelog A.E.: Update 3

Database.cs

- added default Constructor (without any code yet)

- removeLender() DONE
- getRentedCars() DONE
- createLender() DONE
- insertLending() DONE but not Tested yet
- removeLending() DONE but not Tested yet

Lender.cs
- isRemovable() DONE - needed for removeLender() in Database.cs

Others:

- comments added
- DataSet_overview.jpg added (inside the project folder)