Remove redundant entries in application-<DB>.properties in taskana-rest-spring-example-boot

[arolfes]

rest/taskana-rest-spring-example-boot/src/main/resources

Currently there are property files for every supported DB-configuration containing all entries of the application.properties file which is redundant. In Spring Boot you can configure Profiles which will activate the given property-file (e.g. profile DB2 activates application-DB2.properties). This property-file will extend the application.properties file and either adds or overwrites its poperties.

TODO:
Move all common entries into the application.properties file and only keep db-configuration-specific entries in the appropriate files.