Add more features to Thruster Plugin

[acxz]

This issue is a feature request to add specific features to our thruster plugin: https://github.com/osrf/vrx/blob/master/usv_gazebo_plugins/src/usv_gazebo_thrust_plugin.cc

These features are inspired by UUV's thruster plugin: https://github.com/uuvsimulator/uuv_simulator/blob/bfb40cb153684a0703173117b6bbf4258e8e71c5/uuv_gazebo_plugins/uuv_gazebo_plugins/src/ThrusterPlugin.cc

• mappingType of 2, LinearInterp. This allows users to input values from a datasheet and the thrust plugin will linearly interpret b/t them. Example user interface:

<mappingType>2</mappingType>
<inputValues>-1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0</inputValues>
<outputValues>-19.88 -16.52 -12.6 -5.6 -1.4 0.0 2.24 9.52 21.28 28.0 33.6</outputValues>

Example logic:

cmd = 0.9;
(33.6 - 28.0)/(1.0 - 0.8) * (0.9 - 0.8) + 28

• thruster dynamics, first order model
  Example user interface:

<dynamics>
  <type>FirstOrder</type>
  <timeConstant>0.5</timeConstant>
</dynamics>

• minCmd and maxCmd clamping, while maxCmd is already implemented, it is not necessarily being used to clamp the input value.

• maxForceFwd and maxForceRev clamping

Edit: there are more features available in the uuv thruster plugin, such as thruster/prop efficienty and other types of mappings. However, I have only listed the ones that are needed for my specific project. Perhaps another issue such as "UUV Thruster Plugin Feature Parity" may be desired based on community request.