Exclude norm summary sites from history views

- Add WHERE ServiceLevelType <> '' to history views to exclude records
  from sites that send normalised summaries as service level fields will
  be set to default values (empty string and zero) so these shouldn't
  appear in the history views.
Add NOT NULL to primary key hybrid summary fields

- As these fields are part of the primary key, they have an implicit NOT
  NULL condition so might as well make it clear.