Merge state checker

State checker node which subscribes to the odom topic and monitors the odometry. If the robot hasn't moved for more than a set amount of type, it will send an email.

Example usage:
rosrun state_checker state_checker.py _sender:='aaa@bb.c' _password:='***' _receiver:=['first@receiver.com','second@receiver.com'] _email_title:='some title' _email_body='some text' _timeout=90

Note that this works if the sender has an account on gmail (as it uses the gmail smtp email server).