The new site filter breaks links to Maps results, so filter.py needed
to be updated to handle these links as a unique case. A new method was
introduced to easily remove any "-site:..." filters from the query,
which is now also used to format queries in the header template rather
than manually removing the blocked site list within the template itself.
Bumps version to 0.5.1 for releasing the bugfix
Fixes#329
43faaee77f