Add "datamaintain" as a prefix for all the properties keys

[Lysoun]

The properties read by Datamaintain have no prefix currently. For example, the one used to read the db uri is db.uri. It may cause problems if the user's application has also properties named like that. To avoid any collision, a prefix should be added to all the Datamaintain properties keys.

Please change them in

• DatamaintainDriverConfig
• DatamaintainConfig

Once it's done, please ensure that:

• The tests pass. Fix them otherwise
• The samples are not broken because of mismatching properties names
• The documentation is up to date