Necessary website changes before the site moves to pouchdb.apache.org

### Issue

The PouchDB website will move to https://pouchdb.apache.org in the near future. The workflow to build and deploy the site to there is already in place, but the site currently has a variety of new issues that need to be tackled, and we also want to make some structural changes so we can support versioned docs.

This is a super-issue that collects all the necessary steps.

## Apache blocks a variety of external domains, so we need to:

- [x] Remove Gravatar for user avatars and pull the images into the repo.
- [x] Remove Google Analytics.
- [x] Remove Google Fonts and add the fonts to the repo, license permitting (fonts are Lato and Open Sans).
- [x] Remove jQuery entirely or pull it into the repo instead of loading from CDN at `https://code.jquery.com/jquery.min.js`.
- [x] Pull Bootstrap into the repo instead of loading from CDN at `https://netdna.bootstrapcdn.com/bootstrap/3.1.1/js/bootstrap.min.js`.
- [x] Find a way to host `pouchdb.min.js` directly without building it on every site deploy. Currently, pouchdb.com hosts the library itself (from a CDN at `https://cdn.jsdelivr.net/npm/pouchdb/dist/pouchdb.min.js`) so it can be used in the browser terminal. This is a great feature and should be retained somehow.

## Restructure the website so we can have versioned docs

> [!NOTE]
> There is now a PR for versioned docs: #9262

Similar to how the CouchDB docs work, we’d like to have versioned docs. This should probably cover not only the `/api` page, but also `/guides` and `/learn`. We need:
- The default docs anyone sees when arriving at pouchdb.apache.org to be `stable`, eg. the last proper release.
- We also want `latest`, which shows the docs as the are in the `master` branch
- Then we also want versioned docs, eg. `pouchdb.apache.org/8.0.0/api`

We do _not_ need to tie this to the actual release process. All of these pages are written by hand, so we can just create a folder structure that maps to PouchDB releases and change whatever needs to be changed manually. My suggestion for the structure:

**Versioned URLs and their sources (same files as before, but in versioned directories)**
- `pouchdb.apache.org/9.0.0/api` -> `/docs/9.0.0/api.html`
- `pouchdb.apache.org/9.0.0/guides/setup-pouchdb.html` -> `/docs/9.0.0/guides/setup-pouchdb.md`
- `pouchdb.apache.org/8.0.0/adapters.html` -> `/docs/8.0.0/adapters.md`
- etc.

**Latest (points to where the files currently are, in the /docs root)**
- `pouchdb.apache.org/latest/api` -> `/docs/api.html`
- `pouchdb.apache.org/latest/guides/setup-pouchdb.html` -> `/docs/guides/setup-pouchdb.md`
- `pouchdb.apache.org/latest/adapters.html` -> `/docs/adapters.md`

**Stable/default (eleventy should reference/copy those from the most recent release)**
- `pouchdb.apache.org/api` -> `/docs/9.0.0/api.html`
- `pouchdb.apache.org/guides/setup-pouchdb.html` -> `/docs/9.0.0/guides/setup-pouchdb.md`
- `pouchdb.apache.org/adapters.html` -> `/docs/9.0.0/adapters.md`

Existing URLs that are redirected from the old domain would just continue working. We’d also need a version switching widget in a corner somewhere.

This is all doable with stock eleventy, and I’ll give this a go since I have time and a fairly good idea of how to achieve this.