Users can see who updated a performance last.

@christopherThorsen, @GarthGoldwater - Can you take a look at this?  
```ruby
def change
  tables = [:contacts, :customers, :partners, :performances]
  tables.each do |table|
    add_column table, :updated_by, :integer, null:true
    update("UPDATE #{table.to_str} SET updated_by = user_id")
    change_column_null table, :updated_by, false
    add_index_ table, :updated_by
  end
end

could replace all of this