x11/florence: Update to 0.7.2 and adopt

Switch from the stalled SourceForge 0.6.3 distfile to the FrauBSD
continuation on GitHub and take maintainership from ports@.

Drop PORTREVISION, fetch via USE_GITHUB.

Default-on FREEBSD_ORB option replaces the Super key glyph with the
FreeBSD orb (ports-only branding).

Reviewed by: jrm
Differential Revision: https://reviews.freebsd.org/D58428