Add 'inherit_parent_status' option to Fieldmanager_Datasource_Post

`Fieldmanager_Datasource_Post` currently has the `publish_with_parent` option which will publish the "child" posts of the current post when it is published. If the "parent" is then unpublished or trashed, the "children" posts are left published (and might be orphaned). We should consider adding a `inherit_parent_status` option which will trickle changes to children when a parent is published, unpublished, trashed, deleted, etc.

One consideration here is that the one-to-many relationship is not guaranteed. That is, a child post may have more than one parent, which creates a confusing situation. We might want to make it such that a child may only have one parent if this feature is enabled.