Enhance bucket functionality
The bucket mechanism in BridgeDB currently lacks two important features:
a) Only give out bridges that are
fresh, meaning those that have been seen recently enough to be considered worth giving out.
b) Give the user the opportunity to add a number of fresh bridges to a certain bucket pool each time BridgeDB -d is run. This makes it much easier to only mail a delta to a given bridge distributor person plus gives that user a predictable number of new bridges each time.