Backport libreoffice from PPA

Add helper to get latest available version. Libreoffice configures
the ppa to compile for ubuntu focal, and we just have to adjust
slightly the rules to use their work in Trisquel

helpers/DATA/libreoffice/debian-rules.patch

+--- debian/rules	2021-05-29 00:59:51.510029198 +0200
++++ debian/rules	2021-05-29 01:06:26.661451380 +0200
+@@ -595,17 +595,19 @@
+   BULLSEYE_BACKPORT=y
+ endif
+
+-ifeq "$(DEB_VENDOR)" "Ubuntu"
++ifeq ("$(DEB_VENDOR)",$(filter "$(DEB_VENDOR)","Ubuntu" "Trisquel"))
++  ifeq "$(DEB_VENDOR)" "Ubuntu"
+   # Set up Google API keys, see http://www.chromium.org/developers/how-tos/api-keys .
+   # Note: these are for Ubuntu use ONLY. For your own distribution,
+   # please get your own set of keys.
+   # Permission to add API keys, from Paweł Hajdan, To chad.miller@canonical.com
+   # msgid: CAADNaOFSFoch68NM1SGpCTRXqmspyKQgUPUtsF7SGRsRXiHZcg@mail.gmail.com
+   # reused from chromium-browser 48.0.2564.82-0ubuntu1.1222
+   GOOGLEAPI_APIKEY_UBUNTU := AIzaSyDDiKg-iNf3zW2j16KDsnSDnJJAgh4TnCc
+   GOOGLEAPI_CLIENTID_UBUNTU := 424119844901-gee57209rkbo1rgula4i0arilvgv3lsf.apps.googleusercontent.com
+   GOOGLEAPI_CLIENTSECRET_UBUNTU := 3h1DknIrVsq2wEhIuADVxQ3E
+   CONFIGURE_FLAGS += --with-gdrive-client-id=$(GOOGLEAPI_CLIENTID_UBUNTU) --with-gdrive-client-secret=$(GOOGLEAPI_CLIENTSECRET_UBUNTU)
++  endif
+
+   # lp#1034560: MIR troubles make it easier to use internal jfreereport
+   SYSTEM_STUFF := $(filter-out jfreereport npapi-headers, $(SYSTEM_STUFF))

helpers/make-libreoffice

+#!/bin/sh
+#
+#    Copyright (C) 2021 Pablo Correa Gómez <ablocorrea@hotmail.com>
+#
+#    This program is free software; you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License as published by
+#    the Free Software Foundation; either version 2 of the License, or
+#    (at your option) any later version.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program; if not, write to the Free Software
+#    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+#
+
+VERSION=1
+EXTERNAL='deb-src http://ppa.launchpad.net/libreoffice/ppa/ubuntu $UPSTREAM main'
+REPOKEY="83FBA1751378B444"
+BACKPORT=true
+
+. ./config
+
+# Make sure that Trisquel gets compiled same as Ubuntu
+patch -p0 < $DATA/debian-rules.patch
+
+changelog "Backported to get latest version into Trisquel"
+
+compile