Merge SimpleAntiSpam extension into core

Adds an empty, hidden input field to the edit interface, and will
reject any edit if that field is filled in. This will protect
against the simplest form of spambots.

Localized messages will be imported separately.

Bug: 52063
Change-Id: I185b6a1e232299f496244a23f4bf0dc6ea22b6c9
(cherry picked from commit 0988d1200dd5d67719baf076cdbe3e363801ac23)