Add MicroCrystal C7 package

Datasheet: https://www.microcrystal.com/fileadmin/Media/Products/RTC/App.Manual/RV-3028-C7_App-Manual.pdf#page=107

Note that the nominal lead_center_to_center_x = 1.2 is derived from 2.0 - (lead_len / 2) * 2 where nominal lead_len = 0.8.

Footprint MR: kicad-footprints!3680 (merged)