Introduce contact form & map

* privacy.jade: Introduce privacy policy (for contact page).

* layout.jade: Add font weights 400,700,800 for italic variant of the
OpenSans font.

* layout.jade: Improve logic for onfocus/onblur JS action for search
input bar.

* index.js: Re-enable markdown filter and add email_addr var for
passing to the contact page.

* index.jade: Add id field to topics var.

* helpers.js: Rename helper functions from get/set input to get/set
value && introduce additional functions (get_value, null_value, ...).