Update to Gerrit 3.0

A collection of notes for the next Gerrit upgrade.

Issues:

It seems like we need to make sure email sending will work - custom soy templates have changed as far as I understand:

com.google.template.soy.error.SoyCompilationException: errors during Soy compilation
/srv/gerrit/review_site/etc/mail/ChangeSubject.soy:22: error: SoyDoc params are not supported anymore. Use {@param} in the template header instead.
{{ * @param messageClass}}
{{ ^}}
1 errorat com.google.template.soy.SoyFileSet.throwIfErrorsPresent(SoyFileSet.java:1067)
{{ at com.google.template.soy.SoyFileSet.compileForServerRendering(SoyFileSet.java:863)}}
{{ at com.google.template.soy.SoyFileSet.compileToTofu(SoyFileSet.java:747)}}
{{ at com.google.template.soy.SoyFileSet.compileToTofu(SoyFileSet.java:736)}}
{{ at com.google.gerrit.server.mail.send.MailSoyTofuProvider.get(MailSoyTofuProvider.java:97)}}
{{ at com.google.gerrit.server.mail.send.MailSoyTofuProvider.get(MailSoyTofuProvider.java:34)}}
{{ at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:85)}}...