Added defines for db's columns names.
Splited function addNewRemote to addNewDrone and addNewCommandStation.
Refactored addNewSession and deleteSession();
Tables commands_stations and drones now share the same sequence for ids.
Added addNewSessionCentralDrone() and addNewSessionCentralCommand() in DCPServerCentral.
DCPServerCentral add to db commands return the newly inserted line.
Added function getCommandFromCentralSessionId to DCPServerCentral.
Used to check that command station exists and has a sessId with central station.
Added function deleteSessionForCommandId() in DCPServerCentral.
Deleted useless deleteSession() in DCPServerCentral.
Granted read only priviledges to dronedbreader.
Added function deleteCommandById in DCPServerCentral.
Fixed bad SELECT queries in DCPServerCentral.
Fixed bad port argument type in addNewDrone/Command.
Fixed bad WHERE clause in addNewSessionCentralCommand.
Added deleteSessionCentralFromCommandId in DCPServerCommand: deletes command station from sessions_central_commands.
Re-implemented packet handler for central station, using the new db system.