Proposed changes branch

Hi Trent,

I've made some modifications for the code on a separate branch for you to have a look at. I didn't want to mess around with the master branch just yet. 

The changes I've made are mostly for simplifying the code and some for functionality. The summary of the changes are:

1. I changed the for-loop used for streaming the setpoints, to a while-loop which will break when the user terminates the program, or the setpoint is reached.

2. I've simplified the offboard toggle logic, by adding a switch parameter to the function, thereby effectively making the start_offboard() and stop_offboard() functions redundant.

3. I went ahead and placed the functions from offboard_setup.h into their own .cpp file. The functionality is basically the same, but its just seen as better practice.

Furthermore, we may need to decide on a flight-plan for this example, i.e. is the program going to execute when the quad is in the air or on the ground? This may be important for choosing a simple setpoint to work with. So far I've set it to just take off and hover there when the program ends. 

If anything is unclear, please let me know, I'd be happy to explain