text: Title: Draw the projection of the center of gravity on the ground plane
  Body: You'd need to update the following
  **1. The model `VirtualHexapod` to have an attribute that stores this point**
  https://github.com/mithi/hexapod-robot-simulator/blob/531fbb34d44246de3a0116def7e3d365de25b9f6/hexapod/models.py#L95
  
  You can compute this point as outlined by the algorithm here, you should inject the point calculation to a different function and update the attribute of the `VirtualHexapod` when this is called in the two `compute_orientation_properties`  of the `hexapod.ground_contact_solver` module.
  https://github.com/mithi/hexapod-robot-simulator/blob/531fbb34d44246de3a0116def7e3d365de25b9f6/hexapod/ground_contact_solver/helpers.py#L14
  
  **2. In figure template**, you should append a new point trace at the end of the `data` list 
  https://github.com/mithi/hexapod-robot-simulator/blob/531fbb34d44246de3a0116def7e3d365de25b9f6/hexapod/templates/figure_template.py#L226
  
  The trace has the following format 
  
  ```
      {
          "marker": {"color": INSERT_COLOR_HERE, "opacity": 1.0, "size": INSERT_SIZE_HERE},
          "mode": "markers",
          "name": "cog-projection",
          "type": "scatter3d",
          "x": [INSERT_COG_X_HERE],
          "y": [INSERT_COG_Y_HERE,
          "z": [0],
      }
  ```
  
  **3. `HexapodPlotter` could draw this point in the figure template**
  https://github.com/mithi/hexapod-robot-simulator/blob/531fbb34d44246de3a0116def7e3d365de25b9f6/hexapod/plotter.py#L14