Portals; New special page code of "TERMS" which provides a "Terms & Conditions" link on sign-in form

A new special Page Code of "TERMS" has been added.

If a Portal Page uses this code, is active and allows unauthenticated access then a "Terms & Conditions" link will appear in the footer of the Login form. Clicking this will display the page in a modal form.

A new portal.ShowTerms() method has been added to support this.