Version 0.2.5

* detect os in browser and show proper download link (#4173)
* billing: admin can see past due subscriptions
* passwords with umlauts work when logging in after signing up with the
* client (#4002)
* blacklisting common system email addresses listed in RFC 2142 (#3602)
* blacklisting all usernames on the server (#3602)
* configurable blocking of logins in the configuration (#3602)
* require aliases to be all lower-case
* Only allow braintree one-off payments when unauthenticated, & call them 'donations'.
  (#3796)