* drop the ondrej/php PPA since PHP 7.x is available directly from Ubuntu 18.04
* intall PHP 7.2 which is just the "php" package in Ubuntu 18.04
* some package names changed, some unnecessary packages are no longer provided
* update paths
* Install PHP7 via a PPA, enable unattended upgrades for the PPA, and switch all of our PHP configuration to the PHP7 install.
* Keep installing PHP5 for ownCloud/Nextcloud packages because we need it to possibly run transitional updates to ownCloud/Nextcloud versions less than 12. But replace PHP5 packages with PHP7 packages elsewhere.
* Update to Nextcloud 12 which requires PHP7, with a transitional upgrade to Nextcloud 11.0.3.
* Disable TLS cert validation by Roundcube when connecting to localhost IMAP and SMTP. Validation became the default in PHP7 but we don't necessarily have a (non-self-)signed certificate and it definitely isn't valid for the IP address 127.0.0.1.
Merges #1140
[this is a squashed merge from-]
* Install owncoud 9.1 and provide an upgrade path from 8.2. This also disables memcached and goes with apc. The upgrade fails with memcached.
* Remove php apc setting
* Add dav migrations for each user
* Add some comments to the code
* When upgrading owncloud from 8.2.3 to 9.1.0 the backup of 8.2.3 was overwritten when going from 9.0 to 9.1
* Add upgrade path from 8.1.1. Only do an upgrade check if owncloud was previously installed.
* Stop php5-fpm before owncloud upgrade to prevent database locks
* Fix fail2ban tests for owncloud 9
* When upgrading owncloud copy the database to the user-data/owncloud-backup directory
* Remove not need unzip directives during owncloud extraction. Directory is removed beforehand so a normal extraction is fine
* Improve backup of owncloud installation and provide a post installation restore script. Update the owncloud version number to 9.1.1. Update the calendar and contacts apps to the latest versions
* Separate the ownCloud upgrades visually in the console output.
