Add $context to the ArticleFromTitle hook

Add $context to the ArticleFromTitle hook

Most of the time people wouldn't need this - this hook is mostly
used to inject a custom Article subclass for a specific
namespace to do fancy things, but lets give users the most
flexibility.

Asked for by leaves on irc.

Change-Id: I3386ff4abe0e5b3eb783604ae222b7703428db44