Add package dependency graph using graphviz extension

Add a simple package dependency graph, using graphviz.
Use the graphviz Sphinx extension to directly link to the dot file,
instead of manually creating an image file.

conf.py

@@ -29,6 +29,7 @@
 # ones.
 extensions = [
     "sphinx.ext.intersphinx",
+    "sphinx.ext.graphviz",
     "sphinx.ext.todo",
 ]
 

images/package_relationship.dot

@@ -0,0 +1,24 @@
+# to view while editing, use `dot -Tpng package_relationship.dot | display`
+digraph PACKAGES {
+    edge [style=dashed fontsize=10];
+
+    # invisible edge to make the robot_interfaces node appear on top
+    robot_interfaces -> robot_fingers [style=invis];
+
+    entry [label="entry point\nfor users" shape=none];
+
+    entry -> robot_fingers [style=solid];
+    entry -> trifinger_simulation [style=solid];
+    robot_fingers -> robot_interfaces [label="interface\ndefinition"];
+    robot_fingers -> blmc_drivers [label="hardware\ncommunication"];
+    robot_fingers -> trifinger_cameras [label="camera\naccess"];
+    robot_fingers -> trifinger_object_tracking [label="camera + \nobject tracking"];
+    robot_fingers -> robot_properties_fingers [label="forward/inverse\nkinematics"];
+    trifinger_cameras -> robot_interfaces [label="interface\ndefinition"];
+
+    # only for some example scripts, so not really worth adding here
+    #trifinger_object_tracking -> robot_properties_fingers [label="forward/inverse\nkinematics"];
+
+    trifinger_object_tracking -> trifinger_cameras [label="camera\naccess"];
+    trifinger_simulation -> robot_properties_fingers [label="robot model"];
+}

references/package_overview.rst

@@ -7,6 +7,13 @@ Below the main software packages used for to the TriFinger robots are listed.  S
 some additional utility packages from the ODRI project.  Below are only the packages
 that are specifically written for the TriFinger robots.
 
+|
+
+.. graphviz:: ../images/package_relationship.dot
+   :align: center
+
+|
+
 
 - **robot_interfaces** --- [`source <https://github.com/open-dynamic-robot-initiative/robot_interfaces>`__ | :doc:`docs <robot_interfaces:index>`]
       Generic interface for the frontend-backend-system through which the user