Change generated location ros1

[Rick-v-E]

This will change the location of all generated files to $ROS_HOME/virtual_maize_field, which is by default ~/.ros/virtual_maize_field, instead of the world, gt, map and launch folder.

This is needed when converting this into an official ROS package, otherwise these files will be generated somewhere in /opt/ros/noetic/share, which will require sudo to write.

This is however a breaking change, everyone should change their launch file from:

<include file="$(find virtual_maize_field)/virtual_maize_field/launch/robot_spawner.launch">
    <arg name="robot_name" value="<<robot_name>>"/>
  </include>

to:

<include file="$(optenv ROS_HOME ~/.ros)/virtual_maize_field/robot_spawner.launch">
    <arg name="robot_name" value="<<robot_name>>"/>
  </include>

Related: #48

[Rick-v-E]

Close because merge conflict. #55