Use ikiwiki 3.20161219+ instead of our patched one

Originally created by @intrigeri on #12051 (Redmine)

3.20161219 has the needed changes merged in.

Feature Branch: feature/12051-ikiwiki-from-Debian

Parent Task: #5630 (closed)

Related issues

• Related to #11966 (closed)
• Related to #13531 (closed)