Manduca has random_individual. initial_position is 0 centered. optionally record legs/muscles. bugfix when loading time_step

muscle_stength is now part of ManducaBodyProperty. Added mutate/mate methods. Added change_muscle_value method

renamed duplicate tests. Test saving body_properties and loading with fitness_function. Basic tests for simulate().

Also save/load body-properties. distance_traveled is static method. Bugfix: when checking if muscles/legs are already set. Bugfix: record final values when record_level==0. Bugfix: pass kwargs to __init__ in random_individual.

Implemented simulate. Added ManducaBodyProperties. Implemended distance traveled fitness function and added support for custom fitness functions.