[camera] F7 moves CameraFP to robot

fix #443
[hud] add F7 to hud text

TODO use a monospace font for text, not Arial.
TODO increase HUD's height
[builder] scale down Keys_text to fit HUD_plane
[core] Fix the implementation of get_configurations

Return properly the values set, and not only the default configuration
[pymorse] use pure JSON to encode RPC args

`args` is already a list (because of `*args`)
[test] add depth camera test
[builder] Extended significantly the Armature builder helper

In particular, it is now (rightfully) a subclass of actuator, and it supports
adding IK targets to drive specific bones.
Add support for IK in armatures

Kinematic chains can now be controlled via inverse kinematics
by placing/moving so-called IK targets that are tracked by your
armature.

A new service (Armature.place_IK_target) allows to instanteanously
place and orient an IK target, while the asynchronous service
Armature.move_IK_target allows to move at a given speed the target.

The list of IK targets available on a given armature can be obtain
with Armature.list_IK_targets.

To easily create the IK targets, the morse.builder.Armature offers the
create_IK_targets([joints]) that can be called in Builder scripts.

Note that internally, all rotations are handled as quaternions to
ease interpolation over time.

While here:
- removed the IK constraint in KUKA LWR Blend file
- added (from Python) an IK target to the KUKA LWR. Cf
  morse.builder.actuators.KukaLWR
  to see how this is done.
- updated testing/base/armature_testing
[doc] Updated RELEASE notes to mention IK targets
[doc] Mention IK-based (aka, cartesian) control of armatures
[sensor] cleanup Kinect still WIP

The idea is to use ROS' depth_image_proc package to mix depth and rgb
images, instead of converting the OpenGL Depth (Z) buffer to an XYZ
point-cloud, we send a float32 depth image as the kinect does (it sends
uint16 instead, just have to skip `depth_image_proc/convert_metric`[1]).

[1] http://wiki.ros.org/depth_image_proc#depth_image_proc.2BAC8-convert_metric

As mentioned in #419, the launch-file is still a work in progress,
included here as a base for future work.

[#419] https://github.com/morse-simulator/morse/issues/419
[depth] fix DepthCamera default width,height

To be consistent with `morse.sensors.depth_camera.DepthCamera`.
Thanks to Johannes Horvath for reporting on morse-users.
[doc] Rewritten armature creation documentation

Should close #475