Decouple visualization from command language

[marip8]

We should consider simplifying the relationship between tesseract_visualization and tesseract_command_language such that tesseract_visualization does not need to know about specific implementations of the Instruction class. I think there are two options:

1. Eliminate the dependency of tesseract_visualization on the command language Instruction class completely.
   • Instead, the visualization base class could accept "standard" types for display (e.g. vector of poses, tesseract::JointTrajectory, etc.). We would then write conversions from specific types of instructions to these "standard" display types when necessary.
   • See @Levi-Armstrong 's thoughts here
2. Create an over-ridable function to the Instruction class for producing a visualization, like:

   virtual void createDisplay()
   {
     // Base implementation does nothing, but others can override if relevant
   } 

   • Pro: less changes need to be made to support this behavior
   • Con: Adding a function to a base class that is not relevant to every child class is a bit hacky and probably not great practice, even if that function is as simple as an empty void function