make a new NoticeList widget and call it from StreamAction

make a new NoticeList widget and call it from StreamAction

I made a new notice-list widget (like the profile list) and call it
from StreamAction. This cleans up some of the mess in the various
notice-stream-showing classes.

I also changed show-stream so it uses a subclass of NoticeList that
doesn't show author info (which is unnecessary).

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