Use haven for GDPR popup instead of cookieconsent

Haven is newer and more well maintained (and also it is actually
open source instead of open core with an upsell to a paid subscrip-
tion). Haven is configured to be 100% *opt-in* for Google Analytics,
which means it does not load or send a hit until the user agrees.

This is mostly a drop-in replacement, but translations need to make
sure the following strings are updated:

- cookieAccept
- cookieDecline

i18n/bg.yaml

@@ -28,8 +28,11 @@
 - id: cookieLink
   translation: "Научете повече."
 
-- id: cookieDismiss
-  translation: "Разбрах!"
+- id: cookieAccept
+  translation: "Съгласен съм"
+
+- id: cookieDecline
+  translation: "Не съм съгласен"
 
 - id: backToTop
   translation: "Нагоре"