refs #230

- add contributors list to readme and docs' index page
- add CONTRIBUTING.md file redirecting to docs website
- add "translate castopod" section to guidelines

- update js dependencies to latest
- add indentWithTab to xml-editor
- tailwindcss 3.1: replace withOpacity with <alpha-value>

+ update rector config for crowdin compatibility

closes #185

this fixes the adblocker loading viewer error

- rename castopod icons and logos
- fix nlnet logo link
- add castopod icon as logo
- set twitter
card to summary_large_image
- update README.md

- rename podlibre to adaures
- rename castopod-host to castopod
- simplify README and redirect to docs site
- move INSTALL and UPDATE docs
- add new gitlabci pipeline to deploy docs
- upgrade node to v16 in Dockerfile