Add PDF Shortcut (#672)

* Add Blogtrottr as newsletter provider

* Fixed absLangURL issue with sections in footer

* Added embed-pdf shortcode

pdf-js is sered locally to preserve privacy and comply with GDPR

Co-authored-by: Emruz Hossain <hossainemruz@gmail.com>

static/js/pdf-js/web/images/toolbarButton-viewThumbnail.svg

@@ -0,0 +1,4 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><g style="--darkreader-inline-fill:rgba(81, 82, 83, 0.8);" data-darkreader-inline-fill=""><rect x="1" y="1" width="6" height="6" rx="1" ry="1"></rect><rect x="9" y="1" width="6" height="6" rx="1" ry="1"></rect><rect x="1" y="9" width="6" height="6" rx="1" ry="1"></rect><rect x="9" y="9" width="6" height="6" rx="1" ry="1"></rect></g></svg>