Case-insensitive display ordering

This PR changes Student/User ordering by last name to be case-insensitive (some users entered their names all lowercase).  It affects the admin/dev toolboxes, Class roster and assignment pages, and various reports.

Researchers still see [consented] Students sorted by research id.

There is a difference in how the development and production databases treat <code>asc</code> in the following scope in app/models/student.rb:

```ruby
  scope :std_sort, lambda { |user_arg| 
    if user_arg.is_researcher? || user_arg.is_visitor?
      joins{user}.order{user.research_id.asc}
    else
      joins{user}.order{user.last_name.asc}
    end
  }
```
so the code was changed to:

```ruby
  scope :std_sort, lambda { |user_arg| 
    if user_arg.is_researcher? || user_arg.is_visitor?
      joins{user}.order{user.research_id.asc}
    else
      joins{user}.order{lower(user.last_name).asc}
    end
  }
```

to make it more database-agnostic.