blendertools: adapted sensors and controllers to latest blender setup
blendertools: changed layer defs
blendertools: added management of masses in the model
blendertools: added datetime utility function (needed for mass management)
blendertools: fixed problem with child selection routine
blender: added inertial material
blendertools: simplified use of datetime in export
blendertools: fixed mass processing and added to gui
blendertools: added inertial creation function
blendertools: updated update-function to new inertial and mass implementation
blendertools: mass information is now read from inertial exclusively