This commit introduces the term `ddev` for a "Device-SLAM tracked device",
it will be useful to differentiate itself from the `hdev`
("Host-SLAM tracked device") that will be introduced in next commits.
Note that "config_realsense" json field was renamed to "config_realsense_device"
and the device's serial (used for tracking overrides) changed from
"Intel RealSense 6-DOF" to "Intel RealSense Device-SLAM".