Live updates are not respecting Excluded activity settings

[fjarrett]

One of the features of the Exclude tab (see #251) was to also exclude matching records from appearing in the Stream Records (see #223).

However, if you have recent activity already in the DB that is suddenly excluded, those records will come flying in if the Live Update option is turned on.

1. Make some changes to your site to generate a few records
2. Go to Stream > Settings > Exclude and exclude yourself (or your role) from being tracked
3. Visit the Stream Records screen with Live Update enabled
4. At first your activity will be hidden and then suddenly the next live update will bring it in

[fjarrett]

Additional scope was added to this issue in the #362 pull request. We have now added a Visibility option to leave the decision to hide past records up to the user.