Way too many headers in the AlvarMarker(s) messages

[AlexisTM]

Every AlvarMarker message has 2 headers and the AlvarMarkers have (1+2*n_marker) headers.

With multiple header messages, the library developer pushed by laziness will fill only the one which seems to be logic for himself at that time. The app developer will then wonder which one is filled, is it always the same which is filled?

This could easily be solved with a message refactoring.

I would propose the same topology as Pose, PoseStamped and PoseArray:

AlvarMarker.msg

uint32 id
uint32 confidence
geometry_msgs/Pose pose

AlvarMarkerArray.msg

Header header
AlvarMarker markers[]

AlvarMarkerStamped.msg

Header header
AlvarMarker maker