Modified Laser plugin 

added plugin libgazebo_ros_laser_2D.so (modified from
libgazebo_ros_laser) which has time_increment, scan_time and option to
not publish intensities[]. Task #1861

changed lasers' names (links, joints...)
front laser is tilt_laser, back laser is base_laser

changed Gazebo laser's specs according to the datasheets
update rate, noise, angles