Implemented first file encryption
Stored Procedure, Interface changed

I completed the stored procedure in the MySQLDataProvider and changed
some methods in the interface.
File class

File class is extended with a new property and the resource class lost
some code.
Added methods to get a file content
Added database PDF-file

Added the pdf file of the Database graph.
Changed README
Updated .gitignore
Documentation files and MySQL-Script
Removed encryption code

Because of several issues and the fact that we do not support
end-to-end-encryption yet, we removed any file encryption.
Merge remote-tracking branch 'origin/Encryption-AES'
Merge remote-tracking branch 'origin/Encryption-AES'