* include error message from Flattr4j in notification (subText shows message for first failed flattr)
* big extensible flattr notification with full list of error messages

followup on #331
* make FlattrClickWorker drop toast when launched interactively
  as part of a flattr action (by explicitely flattring a thing)
* make it report a notification when it was launched implicitly
  (when refreshing feeds) or when flattring failed

followup on #331