Documentation translation (#199)

Documentation translation using weblate.

* Use po4a to generate .po files from the english markdowns, then to generate translated files
* Some pages can be marked as «english only» (for technical documentation for example)
* New Hugo shortcode to use application strings in documentation (for example for settings names)
* The code of conduct is no more translated, but there is a link to official Contributor Covenant translations
* Adding all plugin's supported languages

Related to https://github.com/JohnXLivingston/peertube-plugin-livechat/issues/117

support/documentation/content/en/credits/_index.md

@@ -0,0 +1,21 @@
+---
+title: "Credits"
+description: "Plugin Credits"
+weight: 90
+chapter: false
+---
+
+[package.json](https://github.com/JohnXLivingston/peertube-plugin-livechat/blob/main/package.json), [COPYRIGHT](https://github.com/JohnXLivingston/peertube-plugin-livechat/blob/main/COPYRIGHT.md) and [LICENSE](https://github.com/JohnXLivingston/peertube-plugin-livechat/blob/main/LICENSE) files contain the license information for this software and its dependencies.
+
+The plugin is maintained by [John Livingston](https://www.john-livingston.fr/).
+
+Thanks to David Revoy for his work on Peertube's mascot, [Sepia](https://www.davidrevoy.com/index.php?tag/peertube).
+The character design is under CC-By licence, and the SVG files used to create some logo and avatars in this plugin are GPLv3.0.
+
+Thanks to [Framasoft](https://framasoft.org) for making [Peertube](https://joinpeertube.org/) possible, for the financial support, and for hosting the project translations on their [Weblate instance](https://weblate.framasoft.org).
+
+Thanks to [ritimo](https://www.ritimo.org/) for the financial support.
+
+Thanks to [Code Lutin](https://www.codelutin.com/) and [Rétribution Copie Publique](https://copiepublique.fr/) for the financial support.
+
+Thanks to [NlNet](https://nlnet.nl/) and the [NGI0 Entrust fund](https://nlnet.nl/entrust/) for the financial support.