Inbox::streamNotices() with deletion compensation: inbox paging should more or less...

Inbox::streamNotices() with deletion compensation: inbox paging should more or less work with deleted items now.
No change in efficiency for the common case where nothing's deleted: does the same bulk fetch of just the notices we think we'll need as before, then if we turned up short keeps checking one by one until we've filled up to our $limit.

This can leave us with overlap between pages, but we already have that when new messages come in between clicks; seems to be the lesser of evils versus not getting a 'before' button.
More permanent fix for that will be to switch timeline paging in the UI to use notice IDs.