This PR adds methods to get an object's inertial parameters in CoppeliaSim to the class 'DQ_VrepInterface' (#109)

* [DQ_VrepInterface] Added properties 'DF_LUA_SCRIPT_API' and 'ST_CHILD' and methods 'call_script_function()', 'get_center_of_mass()', 'get_mass()', and 'get_inertia_matrix()'.

* [DQ_VrepInterface] Modified method 'get_center_of_mass()' to return a DQ. Also simplified how methods 'get_center_of_mass()', 'get_mass()', and 'get_inertia_matrix()' handle their returns from 'call_script_function()'.

* [DQ_VrepInterface] Updated documentation of the modifications.

* [DQ_VrepInterface.m] Scrambled 'call_script_function()' inputs and made it private to match the C++ implementation.

* [DQ_VrepInterface.m] Refactored 'get_center_of_mass()' to have the same behaviour of the C++ implementation. Also added the properties 'BODY_FRAME' and 'ABSOLUTE_FRAME' to match the C++ implementation.

* [DQ_VrepInterface.m] Refactored 'get_mass()' to have the same behaviour of the C++ implementation.

* [DQ_VrepInterface.m] Fixed the way 'get_center_of_mass()' uses 'BODY_FRAME' to match the C++ implementation.

* [DQ_VrepInterface.m] Refactored 'get_center_of_mass()' to have the same behaviour of the C++ implementation.

* [DQ_VrepInterface.m] Fixed error messages of 'get_center_of_mass()', 'get_mass()', and 'get_inertia_matrix()'.

* [DQ_VrepInterface.m] Fixed bug when trying to use 'BODY_FRAME' in 'get_inertia_matrix()' and 'get_center_of_mass()' methods.

Author: ffasilva