redo SDFormat sensor import condition

[jhanca-robotecai]

In the previous implementation, SDFormat <sensor> tag was triggering the import hook based on the sensor type only and it did not use the <plugin> information at all. Now, the hook is matched based on both. In particular:

• a default hook is triggered when no <plugin> is implemented for a particular sensor
• a specific hook is selected based on the <plugin> data if available

This way the user might add their hook with their sensor implementation by using their own plugin name declared in the hook, e.g. it is possible to add a hook for the popular libhector_gazebo_ros_imu plugin.

Tested using three different camera plugins in sdf files, with standard camera plugin:

      <sensor name="camera_test" type="camera">
        <plugin name="camera_plugin" filename="libgazebo_ros_camera.so"/>
        <pose>0 0 0 -1.57 -1.57 0</pose>
        <camera>
          <horizontal_fov>2.0</horizontal_fov>
          <image>
            <width>640</width>
            <height>480</height>
          </image>
          <clip>
            <near>0.05</near>
            <far>15000</far>
          </clip>
        </camera>
        <always_on>1</always_on>
        <update_rate>10</update_rate>
        <visualize>1</visualize>
      </sensor>

without any plugin:

      <sensor name="camera_test" type="camera">
        <pose>0 0 0 -1.57 -1.57 0</pose>
        <camera>
          <horizontal_fov>2.0</horizontal_fov>
          <image>
            <width>640</width>
            <height>480</height>
          </image>
          <clip>
            <near>0.05</near>
            <far>15000</far>
          </clip>
        </camera>
        <always_on>1</always_on>
        <update_rate>10</update_rate>
        <visualize>1</visualize>
      </sensor>

with modified plugin:

      <sensor name="camera_test" type="camera">
        <plugin name="camera_plugin" filename="libgazebo_ros_camera_asdf_super.so"/>
        <pose>0 0 0 -1.57 -1.57 0</pose>
        <camera>
          <horizontal_fov>2.0</horizontal_fov>
          <image>
            <width>640</width>
            <height>480</height>
          </image>
          <clip>
            <near>0.05</near>
            <far>15000</far>
          </clip>
        </camera>
        <always_on>1</always_on>
        <update_rate>10</update_rate>
        <visualize>1</visualize>
      </sensor>

[jhanca-robotecai]

Switching to draft. This PR will be merged after #609 with some more changes.

[jhanca-robotecai]

Force-pushed on top of the #609, waiting for AR in #609

[jhanca-robotecai]

• rebased on top of development due to conflicts (Ackermann model importer hook was added);
• bumped version as suggested by @spham-amzn