Added messages for the mapping to make serialisation easier

Should be able to serialise the segments easily using built in ROS
serialisation. Can store messages in a rosbag written from the node rather than
a topic, and then read back in when necessary.

  # Please enter the commit
message for your changes. Lines starting # with '#' will be ignored, and an
empty message aborts the commit.  # On branch develop # Changes to be committed:
../mapping_msgs/CMakeLists.txt # new file: ../mapping_msgs/msg/MapSegment.msg #
new file: ../mapping_msgs/msg/SegmentPoint.msg # new file:
../mapping_msgs/package.xml # modified: CMakeLists.txt # modified: package.xml #
deleted: src/mapSegment.cpp # modified: src/segmentStorage.cpp #