multimedia/syncplay: Update to 1.6.2

While I'm here:

• Sort variables a bit

Changelog:

• Switched from Python 2 to Python 3
• For all changes since 1.5.5, see:

https://syncplay.pl/changelog/

PR: 235790
Submitted by: Christian Heckendorf <heckendorfc@gmail.com> (maintainer)
Approved by: miwi (mentor)
Differential Revision: https://reviews.freebsd.org/D19278