• New: Support OAUTH2 authentication in a single-sign-on setup in conjunction with roundcube 1.5 OAUTH2 authentication.
  This enables to use the bearer token acquired during login by roundcube to also be used to authenticate with the
  CardDAV server. It is currently not possible to add addressbooks using a custom OAUTH2 provider, i.e. a different one
  than that used to log into roundcube.
• Fix #348: Load the carddav plugin in the calendar task. This enables usage of carddav addressbooks within the calendar
  plugin, for example for the purpose of the birthday calendar.