[ml] Large commit that restructures leg_detector. Defines leg_detector, saved_feature, and matched_feature in separate header and cpp files. Also adds main.cpp, which then starts the process by creating a LegDetector object and then calling ros::spin(). CMakeLists is updated to adjust to the new files and structure as well. More comments are put in, slightly different variable names are used in some cases. Getters and setters are used rather than directly accessing class members. This is the first version that compiles. Needs testing still.