Univention Mattermost app

implements Mattermost 4.4.5
changes behaviour of join/inst script to not wait indefinitely for startup of Mattermost
mysql dump at uninstall is now stored in backup dir as well
fixes the logic of the preinst script to only restore data if Mattermost is not already installed
fixes the ALLOW-FROM header if Mattermost should be embedded in an iframe

implements Mattermost 4.4.2
fixes the nightly backup cron
adds a rewrite rule for .well-known/acme-challenge/ so that certificate requests for Let's Encrypt succeed
add the possibility to specify ssl certificate chain
reset ConnectionSecurity of ServiceSettings back to "None"/empty in case the admin accidentally changed it

implements Mattermost 4.3.1
adds automatic backup of MySQL database through job in cron.daily
adds the ability to configure a custom hostname (and ssl certificate) for Mattermost
queries UCR variables apache2/ssl for custom ssl certificates (and sets it by if no other certificate is given)
makes custom ports in Apache more stable by defining them in the vHost instead
adds a setting to allow embedding Mattermost in other web applications (e.g. the Kopano WebApp Intranet plugin)
fixes logfile location for Apache access.log for Mattermost
optionally enforces verified email addresses for Mattermost users (through app settings)
sets the email address of the Administator user as the address used for outgoing mails

initial release of the app
implements Mattermost 4.2.0
initially creates an Administrator (with a choosen password) user and an Univention team
configures ldap integration
configures mail relay