Change ROI message type to hri_msgs/NormalizedRegionOfInterest2D

[LukaJuricic]

This PR proposed to change the type of the ROI from the standard sensor_msgs/RegionOfInterest to hri_msgs/NormalizedRegionOfInterest2D.

The use of a non-standard message is offset by the following advantages:

• checks on normalized values are image independent and more robust
• algorithms which depend only on the faces/bodies relative position/size and not on the source image can avoid subscribing to the camera info just to obtain the source image size
• aligned with hri_msgs/Skeleton2D which makes use of normalized coordinates too
• NormalizedRegionOfInterest2Dis already part of hri_msgs, let's use it ;)

[severin-lemaignan]

I approve this change.

[clalancette]

We looked at this at the ROS 2 meeting, and this seems like a reasonable change. It is also a subset of #362, so that one will have to be rebased after we merge this.