pep8: comparisons with None

Comparisons to singletons like None should always be done with is or is
not, never the equality operators.
[builder] set {place,aim}_camera deprecated

use set_camera_{l,r}otation instead.
[builder] set simulation camera properties

Make sure the CameraFP has always the same resolution,
and not the one of the last camera added.

Resolution: 800x600, focal: 25mm.
[builder] Set a field _node_name in environment and use it accordingly

In particular, it fixes the code for multi-node scene with cameras.
[builder] allow external node as viewers
[camera] handle multi-node

This fix a crash when adding camera in multinode
[builder] disable Bullet on non logic scenes
[tools] update terrain usage
[pymorse] fix bug of Python 3.2 [Ubuntu 12.04]
[doc] homepages is not persistent
[bin] Fix an now invalid use of prefix

Reported by mirkodaniele dot comparetti at polimi dot it.
[sensor] Fix an incorrect word in odometry documentation

Spotted by Ofer on morse-users@
[doc] Document some missing supervision services
[core] Create local_data with recursive definitions of _data_fields
[doc] Don't store a reference on attribute, but a copy of it.

Otherwise, you will update stuff from mother class, and bad things
happen
[sensor] Add timestamp for sensors

timestamp corresponds to the time computed by the simulator
Moreover, in debug mode, the 'simulator_time' field corresponds to the
real absolute computer time.
[core] Read sensor time from the robot method gettime

It allows to have different robots with different 'bugged' clocks
(timezone, initial shift, slow drift, ...) and use the correct timestamp
tag for each robot.
[sensor] Add a dummy sensor clock
[mw/ros] Prepare ros interface to use the introduced timestamp

The code is not yet activated, because it requires fixing the
computation of timestamp, and requires testing at the ROS level.
[builder] Fix the entry for clock