Use "Content" instead of "Wiki text"

With the introduction of ContentHandler, it's no longer safe to
assume that pages are created with wikitext. In that same line,
the preferred terminology is "content".

P.S. wikitext is one word :-)

Change-Id: I26694c337666982e6d86af7204594afe3bc7f939
Merge "Use "Content" instead of "Wiki text""