Enable visualizing the rotor speed in gazebo

[tongtybj]

What is this

To visualize the rotation of propeller in gazebo

Why

For better intuitive visualization.

Usage

Add independent propeller CAD model which is separated from the link one.
For exmapl:

jsk_aerial_robot/robots/hydrus/urdf/link.urdf.xacro

Lines 236 to 246 in baaa603

	<visual>
	<origin rpy="0 0 0" xyz="0 0 0.032"/>
	<geometry>
	<xacro:if value="${rotor_direction == 1}">
	<mesh filename="package://hydrus/urdf/mesh/propeller/T-motor-CF-14inch-CCW.dae"/>
	</xacro:if>
	<xacro:if value="${rotor_direction == -1}">
	<mesh filename="package://hydrus/urdf/mesh/propeller/T-motor-CF-14inch-CW.dae"/>
	</xacro:if>
	</geometry>
	</visual>

TODO

• update the urdf model of hydrus to enable the visualize

[tongtybj]

visualization sample (hydrus):

hydrus_quad_rotate_visible2_refine.mp4