Rename actions, and related function names

[sugyan]

Originally the action object was for template message only.
But now it is also used for flex message and quick replies, so we should change the name ****TemplateAction.

(Therefore, this is breaking change)

But the interface name TemplateAction is a problem...
I am planning to prepare another interface named QuickReplyAction later, but they do not contain each other. For example, URIAction can only be used with Template and Flex, CameraAction can only be used with QuickReply.

I think that it will become like this form.

type Action interface {
	json.Marshaler
}

type TemplateAction interface {
	Action
	TemplateAction()
}

type QuickReplyAction interface {
	Action
	QuickReplyAction()
}

But is the name TemplateAction strange?
Is there a more suitable name for the interface that can be used in common between Template and Flex?

[suzuki-shunsuke]

LGTM

[sugyan]

Thanks!