Honor *SHOW-LISP-ERRORS-P* and *SHOW-LISP-BACKTRACES-P* when using ERROR-CONTENTS-FROM-TEMPLATE to display errors.

Contrary to the docs the variables `*SHOW-LISP-ERRORS-P*` and `*SHOW-LISP-BACKTRACES-P*` were only in effect when error page was generated using `COOKED-MESSAGE` which is a fallback mechanism.

Another thought regarding `*SHOW-LISP-BACKTRACES-P*` is that, maybe, it doesn't make sense to generate them altogether if `*SHOW-LISP-BACKTRACES-P*` is `NIL`?