filesystems: add new category for file systems and related utilities

The filesystems category houses file systems and file system utilities.
It is added mainly to turn the sysutils/fusefs-* pseudo-category into
a proper one, but is also useful for the sundry of other file systems
related ports found in the tree.

Ports that seem like they belong there are moved to the new category.
Two ports, sysutils/fusefs-funionfs and sysutils/fusefs-fusepak are
not moved as they currently don't fetch and don't have TIMESTAMP set
in their distinfo, but that is required to be able to push a rename
of the port by the pre-receive hook.

Approved by:	portmgr (rene)
Reviewed by:	mat
Pull Request:	https://github.com/freebsd/freebsd-ports/pull/302
PR:		281988

all: remove explicit versions in USES=python for "3.x+"

The logic in USES=python will automatically convert this to 3.8+ by
itself.

Adjust two ports that only had Python 3.7 mentioned but build fine
on Python 3.8 too.

finance/quickfix: mark BROKEN with PYTHON

libtool: compile:  c++ -DHAVE_CONFIG_H -I. -I../.. -I -I. -I.. -I../.. -I../C++
-DLIBICONV_PLUG -DPYTHON_MAJOR_VERSION=3 -Wno-unused-variable
-Wno-maybe-uninitialized -O2 -pipe -DLIBICONV_PLUG -fstack-protector-strong
-fno-strict-aliasing -DLIBICONV_PLUG -Wall -ansi
-Wno-unused-command-line-argument -Wpointer-arith -Wwrite-strings
-Wno-overloaded-virtual -Wno-deprecated-declarations -Wno-deprecated -std=c++0x
-MT _quickfix_la-QuickfixPython.lo -MD -MP -MF
.deps/_quickfix_la-QuickfixPython.Tpo -c QuickfixPython.cpp  -fPIC -DPIC -o
.libs/_quickfix_la-QuickfixPython.o
warning: unknown warning option '-Wno-maybe-uninitialized'; did you mean
'-Wno-uninitialized'? [-Wunknown-warning-option]
QuickfixPython.cpp:175:11: fatal error: 'Python.h' file not found
          ^~~~~~~~~~
1 warning and 1 error generated.

Reviewed by:	portmgr, vishwin, yuri
Differential Revision:	<https://reviews.freebsd.org/D40568>

Remove WWW entries moved into port Makefiles

Commit b7f05445c00f has added WWW entries to port Makefiles based on
WWW: lines in pkg-descr files.

This commit removes the WWW: lines of moved-over URLs from these
pkg-descr files.

Approved by:		portmgr (tcberner)

Add WWW entries to port Makefiles

It has been common practice to have one or more URLs at the end of the
ports' pkg-descr files, one per line and prefixed with "WWW:". These
URLs should point at a project website or other relevant resources.

Access to these URLs required processing of the pkg-descr files, and
they have often become stale over time. If more than one such URL was
present in a pkg-descr file, only the first one was tarnsfered into
the port INDEX, but for many ports only the last line did contain the
port specific URL to further information.

There have been several proposals to make a project URL available as
a macro in the ports' Makefiles, over time.

sysutils: remove 'Created by' lines

A big Thank You to the original contributors of these ports:

  *  <jsmith@resonatingmedia.com>
  *  Aaron Dalton <aaron@FreeBSD.org>
  *  Aaron Landwehr <aaron@snaphat.com>
  *  Adam Weinberger <adamw@FreeBSD.org>
  *  Adrian Chadd
  *  Adrian Chadd <adrian@FreeBSD.org>
  *  Akinori MUSHA aka knu <knu@idaemons.org>
  *  Alan Eldridge <alane@FreeBSD.org>
  *  Alan Eldridge <alane@geeksrus.net>
  *  Aldis Berjoza <aldis@bsdroot.lv>
  *  Alex Deiter <alex.deiter@gmail.com>

sysutils/py-prometheus-zfs: Update to 1.0.4

sysutils/py-prometheus-zfs: Initialize rcvar

The rcvar (zfsprom_enable) must be initialized. Otherwise, rc(8)
complains with the following message:

    /etc/rc: WARNING: $zfsprom_enable is not set properly - see rc.conf(5).

sysutils/py-prometheus-zfs: Add KEYWORD:shutdown

sysutils/py-prometheus-zfs: New port

Prometheus exporter for ZFS statistics using py-libzfs.

WWW: https://github.com/matusnovak/prometheus-zfs