Lowers the jquery-ui-rails dependency.

This fixes an issue with engines like Alchemy CMS that use jQuery UI 1.9 and can't update because jQuery 1.10 is broken right now. See http://bugs.jqueryui.com/ticket/9166

Since Spree does not need jQuery 1.10 and works great with jQuery UI 1.9 I think its a good idea to lower the dependency. Projects that want use jQuery 1.10 are free to use it, this change only allows projects to use spree with jQuery UI 1.9.
make sure we load the promotion rules after initialize so the user
rules are correctly saved.
also remove the after_save on promotion, this is no longer needed.
Only count eligible promotions towards Promotion#credits

Fixes #4120