Implement an set_armed service in drone_control

[AlexanderWangY]

Depends on #7

Create a ROS service in common_srvs to arm a drone.

There should be 2 functions, one for setting the armed to either true or false, then a callback called arm that accepts a value to either arm or disarm. The service should accept a CommonBool or something to that effect. true for arm, false for disarm.

Return a true or false for successfully armed/disarmed or failed to execute.

Test this through rosservice call