Optimize descritpion to be usable also remotely

[destogl]

For the remote access fo the robot description, e.g., when running software on the robot and showing data on a remote computer, we need to use package://-form of accessing meshes to have paths resolved properly. Therefore we need to all this snippet to our templates:

<xacro:if value="${simulation}">
      <xacro:property
        name="file_prefix"
        value="file://$(find maha_description)"
        />
    </xacro:if>
    <xacro:unless value="${simulation}">
      <xacro:property
        name="file_prefix"
        value="package://maha_description"
      />
    </xacro:unless>

and then use <mesh filename="${file_prefix}/meshes/ everywhere.

[Nibanovic]

I've addressed this in a commit in gazebo_template PR, as it already has gazebo set up for me to test this.

Test:

Added the flag, generated the description package and added a dummy base_link.stl into the generated package.

Expectations:

Launching both regular and gazebo bringup should spawn with base_link.stl as geometry, without any errors from Gazebo

Result:

Everything works as expected