Add sym/cmp for crystals with a grounded case

[ii8]

SUMMARY

add crystals with ground connection

CHECKLIST

• I have read and followed the library conventions¹.
• I already used the new library elements in a design and verified their correctness (optional).
• I'm the copyright owner of the added content (i.e. the changes are made by myself, not copied/imported from somewhere else).
• I agree to publish all my changes under the CC0 Public Domain License³, allowing everyone to use and modify the content without any restrictions.

¹ Library Conventions: https://docs.librepcb.org/#libraryconventions
² Minor version bump if only metadata was modified (e.g. "0.1" -> "0.1.1"), major version bump if functional changes were made (e.g. "0.1" -> "0.2")
³ CC0 Public Domain License: https://en.wikipedia.org/wiki/CC0

[ubruhin]

@ii8 Thanks for this contribution and sorry for the delay! Just one quick question: Do you have any objections in making the symbol more compact and keeping the same orientation as the other crystal symbol?

(Maybe some day we should rotate them both to have GND at bottom, but the project library updater is not able yet to auto-correct the rotation after an update so it's better to keep the rotation of the existing crystal for now.)

If you're fine with this change, I'd commit it and merge this.

[ii8]

Yea that's fine