Rename new columns to allowcomments, approvecomments for consistency with view & artefact tables
Add approvecomments column to view & artefact tables
Move all view_access_usr, view_access_group, view_access_token records into an expanded view_access table
Drop view_access_usr, view_access_group, view_access_token

Signed-off-by: Richard Mansfield <richardm@catalyst.net.nz>