[builder] Provide a set_camera_speed method

Call it by default in the environment ctor, so the camera has a
reasonnable speed by default (reported by Marc Hanheide).
Part of #405
[actuator] Improve light actuator

Provide properties to configure size, distance, light color and energy
Update the doc
[actuator] add a service to toggle the light
[builder] add a set_color method
[builder] Add some argument to environment to disable auto renaming

The default behaviour is still to do magic renaming by default.
Contributed by Felix Meßmer
[builder] Introduce two new basic objects: empty and cordsys

From Felix Meßmer
[builder] Rework implementation of add_default_interface

The new implementation only adds the default service and datastream
entry if the sensor | actuator does not get already some service or
datastream configured for this specific middleware. Moreover, it now
handles properly the sensors and actuators added after the call of
add_default_interface.

It should fix #399 (but people interested by the features must test to
see if it matches their expected semantics).
[builder] Update deprecated overlay function in pr2 description
[ros] Fix double self-reference
[human] Reload scene when human is used
[cmake] Force the python executable when lauching sphinx-build

Fix some build issue when both python2-sphinx and python3-sphinx are
installed. Reported by M. Bulk from robotpkg.
[builder] Fix minor bug introduced in 01d8c708b21d25ead
[builder] Makes the selection of Morsy color more robust with several instances

Accounts for Blender autorenaming Morsy material (ie, body.001,
body.002...)
[sensor] Do not crash when using cameras in fastmode

Instead, display a gentle warning.

While here, slightly improve performances of camera by skipping useless
test once the camera is setup.
[builder] Add a method to configure the logger level at builder level

Close #337
[doc] Sync what_news and RELEASE_NOTE with current state of Morse