- added to the class `ISqlDatabaseBackend` the ability to delete a sql table
- also added `SshAccessedMysqlDb`: an implementation of `ISqlDatabaseBackend` that implements the sql database as a remote sql database accessed using ssh
- added unit tests to validate the backends SshAccessedMysqlDb and SqliteDb
work related to [https://bugzilla.ipr.univ-rennes.fr/show_bug.cgi?id=3958]
