Trigger test

[Wilhelm-Marais]

Initial implementation for trigger over ethernet with action commands. Enables synchronisation of multiple cameras using only a single cable.
Test Instructions:
-Set camera trigger_source to Action0 with action keys and masks all set to 1 (see stereo_camera_two_nodes.launch for an example)
-Run the trigger_node using 'rosrun trigger_node x' where x is the desired trigger frequency in Hz, eg 20
-Test the frequency of the incoming frames using 'rostopic hz'
-For a rough test of synchronisation for a stereo pair, a stopwatch on a phone can be held in front of the cameras and corresponding image pairs compared

[icolwell-as]

Thanks @Will-Marais for the PR!
You will need to resolve the merge conflicts before we can proceed with reviewing and merging the PR.
Also, can you update your PR description with brief testing instructions? Basically just need to explain how to test the code in this PR. We have an ethernet Mako camera which we can test on.

[icolwell-as]

@Wilhelm-Marais, thanks for submitting this! I was able to test action-based triggers with our Mako camera. I can't get your trigger_node to work, but I've found a good example in the Vimba SDK that I plan to use to re-implement this trigger_node idea (the example uses the VimbaCPP API instead of VimbaC API as you have used).

Thanks for laying the groundwork and demonstrating how this could work! I'll leave this PR open until the refactored version is merged into master.

[icolwell-as]

This functionality was merged in PR #39
Thanks again!