Consolidate common code in micro-apps custom notice type display actions.

Consolidate common code in micro-apps custom notice type display actions.

The ShowNoticeAction subclasses were cut-n-pasting a lot of prepare() code from ShowNoticeAction, though the only part that's different is how we look up the notice. Broke that out to a getNotice() method, so only that needs to be copied. Avoids extra copies of permission checks and other common code in this spot.