Drop graphviz dependency from tf

[jschleicher]

It would be nice to split view_frames into a new package tf_tools or similar to get rid of the graphviz dependency on headless systems.

(Similar to ros/actionlib#129)

[tfoote]

Since tf is deprecated for tf2 and in tf2 we've cleaned it up to use tf2_tools for the graphical tools.

As that cleanup was done as part of the refactor for tf2 I don't plan to refactor this package but recommend migrating to use tf2/tf2_ros which included a significantly reduced dependency footprint in it's design.

[jschleicher]

@tfoote Thanks for the hint (I should know, that tf2 is the recommended package): In melodic is robot_state_publisher and rviz, that still pulls in tf in my setup, so I'll open issues over there.