BC: Rename boolean methods of PlanSubscription

[Konafets]

I propose the renaming of the following methods from PlanSubscription:

• active() to isActive()
• onTrial() to isOnTrial()
• canceled() to isCanceled()
• ended() to hasEnded()

This has two reasons:

1. It is a convention to have these kind of methods prefixed with is or has
2. The current naming interferres with the scope feature. I want to create a scope scopeCanceled() which will be used like this:

$canceledSubscriptions = Subscription::canceled()->get();

I can not do that currently because of the canceled() method. This will be called instead of the scope.

This is a BC break.

[gerardojbaez]

I agree, can be added for v2.

Thanks!