Headphone Hook improved for different shelf thickness

This thing is an improvement/remix of the one made by "Misguided" on Feb 9, 2011.
http://www.thingiverse.com/thing:6256

The original design allows to hang the headphones under your office desktop. This new remix is based on the version 4 of his short and large hooks models, that have the bracket bend inwards slightly to reduce some of the sagging of the bracket under load.

This new remix includes the following improvements:

- The lower lateral arch has increased its height to provide more protection to the headphones because with the original design I noticed that the headphones used to fall down if a near chair hit accidentaly to them. With this new protection the probability of falling down has been reduced.
- The large and short hooks now have the same thickness in the sides of the bracket bend. They have been equalized to give more sturdiness to the whole structure.
- The lower corner of the bracket bend has reduced its radius. Now it is equal to the upper corner. It sh