Add video to splashpage

[davidsf]

We need to add an option to Splashpage page in the admin with a youtube url and a checkbox to show/hide the video from the splashpage.

• Migration to add a boolean field include_video and text field video_url to splashpages table
• Add controls to the admin splashpage.
• Add partial to show the video in splashpage.

[linuxonrails]

I think we should add the link to the free format video. Not a YouTube link.

Or... a YouTube alternative (https://invidious.io/)

[davidsf]

I was thinking about using peertube.

Maybe it's better to support both platforms for the splash video.