www/webgrind: Update from 1.4.0 to 1.5.0

[joneum]

Summary

• www/webgrind: Update from 1.4.0 to 1.5.0
• Changes:
  • Allow custom CSS
  • Miscellaneous bug fixes

PR: 219884
Submitted by: Franco Fichtner (maintainer)
Approved by: xxx (mentor)
#Differential Revision: https://reviews.freebsd.org/Dxxxxx

Test Plan

~/dev/ports/www/webgrind % portlint -AC
WARN: Makefile: for new port, make $FreeBSD$ tag in comment section empty, to make SVN happy.
0 fatal errors and 1 warning found.

poudriere testport:

10amd64
10i386
11amd64
11i386
12.0-CURRENT r318899 amd64
12.0-CURRENT r318400 i386