Fix UI and Update issues

[mariobehling]

1. Fix missing images and ensure all media files come from internal resources (not external)
2. Unlink Streamboxx page https://voicerepublic.com/pages/streamboxx. We currently don't provide this feature but might come back to it later again.
3. Update dead/outdated links to blog, help, etc. e.g. to Twitter it should be https://twitter.com/VoiceRepublic_
4. Delete tawk.to box service
5. Fix links to public pages
6. Take out Facebook Login (comment out the code in case we come back later)
7. Fix RSS issue resulting in a lot of resource usage
8. Add a privacy respecting captcha for user sign up
9. Check validity of https://github.com/voicerepublic/voicerepublic_dev/blob/integration/CONFERENCE.md and move any still relevant content to Readme.md. Then delete file.

[mariobehling]

In regards to privacy respecting captcha an option seems to be hcaptcha https://www.hcaptcha.com/