Add grounded crystals to SparkFun-FreqCtrl.lbr

[This is renewed pull request #38, cleaned up and now on a feature branch.]

In many designs today it is good to have the crystal case grounded, to reduce noise.

This pull request adds a grounded crystal device, CRYSTAL_WITH_GND, the corresponding symbol Q_WITH_GND, and an example package CRYSTAL-SMD-3225-GND.

This pull request does NOT move some of the existing packages from CRYSTAL to CRYSTAL_WITH_GND. However, most probably that should be done, as some of the packages in the current CRYSTAL device do have ground pads for grounding the case.