Add a way to insert a site-wide message under the mega-menu. To turn on the message set the configuration value:

canada.show_site_message = True

and fill in the snippet files:
ckanext/canada/templates/public/snippets/site_message_en.html, and
ckanext/canada/templates/public/snippets/site_message_fr.html

Used for BH Ticket No. 670
Merge remote-tracking branch 'vb1/wet4-gcweb' into wet4-gcweb
Add custom 404 for Canada.ca
Merge remote-tracking branch 'vb1/wet4-gcweb' into wet4-gcweb
Update custom 404 and megamenu for Canada.ca
Merge remote-tracking branch 'origin/wet4-gcweb' into wet4-gcweb
Update footer (and README).
Update to WET 4.0.9