[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
[builder] Add an entry for ROS for the PTUPosture sensor

Spotted by Lars Kunze
[bin/morse.in] 2.68 seems ok for Morse!
[actuator] new 3D sound
[sound] enable 3D effect using activate()
[geolandloader] remove Blender 2.4x code
[tools] new terrain creator tool (geotiff/dtm)
[release_notes] add a row on 3D sound actuator
[release_notes] add terrain tools notes
[ci] travis: exit on error

use `bash -e` to exit the script on error