MWException: Fix sitename appearing twice in <title>

MWException: Fix sitename appearing twice in <title>

The MWException::getPageTitle method is wrapping the page title
in the 'pagetitle' ($1 - sitename) message, but OutputPage does
this as well when outputing <title>.

OutputPage::prepareErrorPage takes the first parameter as page
title (unwrapped, appears in <h1>,) and the second optional one
is for <title>, which (if omitted, like before) results in
pagetitle being applied by OutputPage.

Now that we specify them separately, this also removes the
sitename from the <h1> on the page, which always looked weird.

It also fixes DBQueryError (extends MWException) where previously
no sitename was added, it just returns 'databaseerror' from
its DBQueryError::getPageTitle() method.

Change-Id: I85d65d89e72b4497a050f440524ff6f959518b88