seo changes

[recluse4615]

(i need to redo this branch, because i based it off of my local modal branch and it's pulling in likely incorrect commits)

current changes:

• adding in json-ld for individual packages (incl. reviews)
• adding in breadcrumbs for most pages (mostly as a nicer UX, but also json-ld breadcrumbs)
• adding self-canonicalisation to some pages (need to expand this to other pages)

most of this pr is fine to go straight to production, but would mostly appreciate feedback on implementation/changes to make (i have next to no experience w/ python and absolutely none with flask)

changes i want to work on:

• expansion of opengraph data where possible
• more json-ld data where needed (flat pages = article, etc)
• friendlier urls instead of /packages/?type=txp (a bigger task since we can have them as extra home pages..)
• canonicalisation of other pages
• moving locales to different directories, eg /en-us/, /fr-fr/