Revert "Revert "Merge branch 'master' of git.ece.iastate.edu:danc/MicroCART_17-18 into batch-setpid""

This reverts commit b9292f1c.

Yes, this is a revert-revert. Brendan broke all the things.

This reverts commit 293b9d07

- removed every use of the "subtype" term
- made the "type" term 16 bits
- made sure that every reference to a message type is 16 bits and used correctly
- simplified commands enum names
- implemented setcontrol callback function that switch on the controller and P, I, D, setpoint value to be set and then set them
- partly implemented getcontrol callback function
- NOTE: setpoint is a double. this causes some problems..
- TODO: add setpoints for rate controllers
- TODO: figure out what message ID I should send back when I get a getpid command

Integrated changes from comm_dev (interrupt-driven UART) and updated code to work well with the new style. Compiles, but have not tested running yet.