Break early when building cross repository activiy streams

Cross repository activity streams cause all repositories to be opened which can take a long time for huge numbers of repositories (some customers have >1900).

Using the last write time, activity items should be fetched sequentially youngest to oldest and it should break as soon as enough items have been collected and/or a configurable timeout (default to say 10s) is reached. In the case of a timeout print a message to the stream indicating all items were not fetched.