forms: don't use secure forms with authentication token for GET requests

The token is secret and should never be used in forms posted with GET which are
URL encoded. aef21d16a262 was too aggresive in using secure forms everywhere
and did thus also incorrectly use them for forms posted with GET.

Some token leakage was reported by Gjoko Krstic <gjoko@zeroscience.mk> of Zero
Science Lab.