Refactor component position assignment

[a-barbieri]

Fixing one of the performance bottolenecks listed in issue #211. Now it's 40% faster!!

A database schema update is necessary:

1. Create a migration from terminal

rails generate migration updateComponentPositionDefault

2. Add the following line between def change ... end in db/migration/0000_update_component_position_default.rb (you probably don't have the 0000 sequence)

class UpdateComponentPositionDefault < ActiveRecord::Migration[5.2]
  def change
    change_column :binda_components, :position, :integer, default: 0
  end
end

3. Run the migration in your terminal

rails db:migrate