Check 'order.active' instead of hardcoded Order states

[heiko-r]

Currently, OrderService.cancelOrderById() and OrderService.cancelOrderByOrderLines() check if (order.state === 'AddingItems' || order.state === 'ArrangingPayment') to determine whether the Order can be cancelled or not:

• https://github.com/vendure-ecommerce/vendure/blob/master/packages/core/src/service/services/order.service.ts#L1027
• https://github.com/vendure-ecommerce/vendure/blob/master/packages/core/src/service/services/order.service.ts#L1058

Due to this, OrderService.cancelOrder() cannot be used with a customised order process, such as when the order is set to active: false and stock allocated in ArrangingPayment state already.

Suggestion: Use order.active instead of comparing order.state to hardcorded states.