Create Static Transform Broadcaster and publish flange->tool0 to newly created /tf_static topic

[jimmy-mcelwain]

In reference to #20

[jimmy-mcelwain]

This successfully publishes flange->tool0 to tf_static, but I need to do more testing and probably clean it up

[gavanderhoorn]

Nice work.

A high-level comment and a question:

• would there be a way to implement this without adding more static variables? Some of the added functions don't take any arguments but just edit static variables. I understand why you did that, but I'd suggest trying to move away from that pattern, as it facilitates testing (can just pass in 'test values') and reduces potential for problems.
• is the bool check has-this-been-sent-yet really needed? I was hoping the static transform broadcaster would be smart enough to not broadcast transforms it's already seen, or we can just call send(..) once outside of the loop, right after the agent connected. It would be OK to republish in case of a dropped connection / a reconnect. tf_static is for 'never' changing transforms -- or things that change very infrequently, so republishing is acceptable.

[jimmy-mcelwain]

I will look at those suggestions. I added static variables because that is how it is done with the other PositionMonitor messages and publishers. I can probably switch off of static variables. As for the check has-this-been-sent-yet, I can probably find a better way.