Trilateration ROS package.

Implementation of different trilateration localization algorithms:

• Linear trilateration
• Nonlinear trilateration
• RANSAC trilateration (TODO)

Modified to be compatible with the GTEC solution:

• Ranging messages are now gtec_msgs::Ranging (https://github.com/valentinbarral/rosmsgs)
• There is a new subscription to receive the anchor positions using a publisher like the node anchors included in:https://github.com/valentinbarral/rostoa.
• The output is now a PoseWithCovarianceStamped.
• Tested and working in simulation using https://github.com/valentinbarral/gazebosensorplugins.

Trilateration test: https://user-images.githubusercontent.com/38099967/109551631-155b7180-7ad1-11eb-9b51-e394b99d83fb.mp4