[Feature] Add support for lunar calendar

[ngocanhtve]

Asian countries use the lunar calendar. And because the family tree will record the date of death as a milestone to organize the death anniversary, the lunar calendar is required.

Therefore, please add a lunar calendar system (if technically possible) so that Asian users can more easily use the application.

[michelesalvador]

Please help me understand better which functionalities of Family Gem would be involved on supporting the lunar calendar.
Maybe:

• Enter date in event detail with lunar calendar spinners?
• Display age following east asian age reckoning?
• Notify annual anniversary of death date?
• Else?

[ngocanhtve]

• Notify annual anniversary of death date?

This is it. This is extremely important.