mediawiki: use sites-available everywhere.

Also, we add an updated header to the redirects.conf file and import
the corresponding .dat file and the generator. This way redirects.conf
can be generated from the .dat file and submitted for review.

Change-Id: I42a07252bf6ed37231ecba587e8dfc018e5c6609
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>