Send Super Users an email when a new Piwik version is available

[mattab]

To increase upgrade rates of Piwik users to the latest version, we can notify all Super Users from a given Piwik when there is a new Piwik release available to download.

The email will be sent to all super users when Piwik detects a new stable version has been released.

Proposed requirements:

• we only email for new stable core releases
• we do not email for plugin upgrades
• emails are sent only once per Piwik version (to all Super Users)
• the notification can be disabled in the configuration file (no need for UI to disable email notification)

[mattab]

Proposed email (possibly to improve?)

Dear Piwik user,

'ThereIsNewVersionAvailableForUpdate'

'YouCanUpgradeAutomaticallyOrDownloadPackage'

Click here to update Piwik now!

[hpvd]

maybe a notification for new beta versions is also interesting:

• feedback for new versions can start earlier if users upgrade earlier
• could reduce number of tickets for things which are already fixed in the new version (because they upgrade earlier)
• may help security (even in beta version)

could be implemented in the config file like this:
"upgrade notification: final, beta"

[hpvd]

same 3 reasons may fit for plugin new version notification...
=>
config file
"piwik upgrade notification: final, beta
plugin upgrade notification: on"

[hpvd]

hmmm don't know but
maybe this notification settings can also be used for notification within piwik (upper right corner)?

=> set it to "beta" on the test server one could receive a notification for new betas even if the installed testing version is final (because this was the latest available version)...

[tsteur]

In 1a1c50a: fixes #4843 send email notifications to all super users in case of new Piwik core update and/or Marketplace plugin updates. Core update email notifications are enabled by default and can be disabled in config. Plugin update notifications are disabled by default and can be enabled in UI -> General settings

[mattab]

In 535c802: Refs #4843 adding default From: to emails