Mjbots behavior loop and example

[ethanmusser]

A class extending MjbotsControlLoop to compose a kodlab::BehaviorManager object and wrap some of the BehaviorManager's functions. This is intended to be extended by the user and act as the main control loop.

• Provides an MjbotsBehaviorLoop class in the kodlab::mjbots namespace that holds a kodlab::BehaviorManager object.
  • This object extends MjbotsControlLoop and maintains the same template and intended implementation.
  • The MjbotsControlLoop Update method is overridden to call the BehaviorManager Update, which itself calls the Update's of the selected behavior (as well as handling their Begin and Stop methods).
  • Provides wrappers for the AddBehavior and SetDefaultbehavior functions of the composed BehaviorManager which automatically include the shared pointer to the RobotBase-derived robot.
• Provides an example of a user-implemented behavior loop which maintains several custom behaviors and demonstrates switching between them via LCM input.

This implementation has been tested with the behavior_robot_example.cpp example provided, which uses the various example behaviors provided in #39.

Note that this PR is 3/3 in the behavior implementation series and depends on the Behavior class introduced in #39 and the BehaviorManager class introduced in #40.