Added daily routine to executive

This adds the ability to set up a daily routine for the robot such that the same tasks are proposed to the scheduler every day, and for appropriate subwindows within this. 

It's behaviour can be seen by running `rosrun task_executor example_task_routine.py` in conjunction with either of the existing task executors. As it stands there is still a bug in the scheduler code which makes it not handle all times correctly. Things should run ok still though.

This closes #15