New persistence handler

P/Sda1/persistencehandler/.gitignore

P/Sda1/persistencehandler/pom.xml

.../de/hdm_stuttgart/mi/sda1/persistencehandler/DbProps.java

...ttgart/mi/sda1/persistencehandler/PersistenceHandler.java

..._stuttgart/mi/sda1/persistencehandler/database.properties

P/Sda1/persistencehandler/src/main/resources/log4j2.xml

P/Sda1/persistencehandler/src/main/resources/schema.sql

...hdm_stuttgart/mi/sda1/persistencehandler/PersistTest.java