particular embodiment the slide 393 is provided additional support and guidance from a right guide rod 381 and a left guide rod 383 fig4 shows an exploded perspective view of the first embodiment of the invention 101 the wall of aperture 335 in the retaining block 333 linearly guides the sliding support arm 311 one or more magnets 337 frictionally engage sliding support arm 311 providing resistance of movement of the sliding support arm 311 through the retaining block 333 the magnets 337 fit within lateral apertures 339 the magnets 337 are covered by plugs 341 preventing removal of the magnets 337 once the unit 301 is assembled the swing arm 331 is pivotally connected by a hinge 389 to the elongated chest piece 367 the sliding support arm 311 is pivotally connected to the swing arm support 321 by a pin 315 passing through an aperture 313 in the sliding support arm 311 a lower aperture 323 in the swing arm support 321 receives a portion of the pin 315 the upper portion of the swing arm support 321 is pivotally connected to the elongated chest piece 361 by an upper pin 327 passing through an upper aperture 325 in the swing arm support 321 and an aperture.