[sensor] Fix compound sensor, which was broken by timestamp addition

We previously test against "local_data" to be empty, which is never the
case nowadays, as it always contains at least a timestamp. Use a
specific flag to check for late initialization.
[ros] refactor pose publishers and add PoseWithCovarianceStamped

[ros] pose: only publish if data is marked as valid

if the sensor data does not have a valid field, always publish
[ros] read_pose: add PoseStampedReader
[ros] read_pose: also set position and orientation

as mathutils Vector and Quaternion respectively
[ros] pose: use functions instead of PosePublisherHelper class
[ros] Check if 'valid' is present instead of relying on exception handling

Reported by Pierrick
[ros] pose: check key in dict instead of try..catch
[testing] Fix pr2/joinstate_socket fallout from timestamp addition
[ros] fix PoseStampedReader
[helpers] transformations: add setters for rotation and translation
[actuators] teleport: consider actuator2robot transformation
[ros] sematic_cam: consider relative option for frame id

If the relative option is used the default frame_id is the name of the
component, otherwise /map as before You can also overwrite the frame_id
by explicitly specifying it.

fixes #515
[camera] Add scene only if the camera is owner by an 'internal' robot

Fix #526

The semantic of bge.logic.addScene is crappy (and I'm generous). If the
scene does not exist, it still do something, which seems basically
duplicate the current scene, with all the logic. It is a problem in the
multinode case where only the scene related to the controlled robot are
created.

Still, it is definitively not a good fix, as it leaks multinode
abstraction in a component. The 'good' solution would be to 'not
configure' component owned by external robot (instead of configure, then
disable), but last time I tried that, it seems a lot more harder than
expected.
[doc] Tweak phrasing in some docs where the language doesn't flow
[multinode] fix finalize when no master connected
[builder] Don't abuse _blender_filename to configure modifier

Use the classpath of the associated component, as done for datastream.