fix placement of URDF objects with inertials
fix problem of unsolvable defaults for mass in urdf fake objects
got rid of mysterious motor "DX117"

This one even goes back to the old MARS SVN and even though
it seems to have been meant to model a Dynamixel DX117,
it was implemented as a crippled DC motor.
add backwards-compatible loading of motor type strings
load SMURF-bitmasks in MARS