Add a way to prevent a term from being deleted

[wpsmith]

Currently, WordPress uses an option ('default_category') to prevent the deletion of the default WordPress category. However, someone creates a default term for a custom taxonomy, there is currently no easy method to prevent the deletion of the term.

I propose a simple filter that would enable this.

Just saw this in WP_Terms_List_Table:

$default_term = get_option( 'default_' . $taxonomy );