tf2_gemometry_msgs as a dep for vn_sensor_msgs; try/catch readGpsCompassBaseline

[jfinken]

Changes:

• Add tf2_gemometry_msgs as a dep for vn_sensor_msgs
• try/catch around readGpsCompassBaseline()

Addressing:

• issue 58
• issue 57

[dawonn]

Thank you very much for the PR, it's incredibly appreciated!

[dawonn]

I'm guessing that the get GPS baseline function should only be called if it's a VN300. It would be super cool if you could wrap that in an if statement that checks that the device is a VN300, that way VN 100 and 200 users aren't seeing error messages that don't pertain to them.