Add mysql persistence service

This is fundamentally a combination of the existing sql persistence service, and the mysql driver. The driver has been updated to the latest version. The current persistence.sql and persistence.sql.mysql should be deleted.

This has been discussed elsewhere.

To convert from the current service to the new service, perform the following steps -:
Rename configurations/persist/sql.persist to mysql.persist

In openhab.cfg
persistence:default=mysql
Remove the line -: mysql:driverClass=com.mysql.jdbc.Driver

Change the following from sql:x to mysql:x
mysql:url=
mysql:user=
mysql:password=