Switch to actively maintained Fomantic-UI (backwards compatible)

[lubber-de]

Semantic UI has'nt been maintained since 2018, but the active community fork https://fomantic-ui.com already got 500 bugfixes and new features like calendar, slider, toast, etc.

it is backward compatible, the current code should work as it is.

https://fomantic-ui.com
https://github.com/fomantic/fomantic-ui

[iamareebjamal]

Yes, we've planned to try it out and will soon comment if we need any help. Thanks a lot for reaching out :)

[iamareebjamal]

We tried fomantic UI here fossasia/open-event-frontend#4538 but it caused modals (fomantic/Fomantic-UI#1590) and nested popups to break fossasia/open-event-frontend#4730 and fossasia/open-event-frontend#4735

So, we cherry-picked the fix for scroll lock from this PR fomantic/Fomantic-UI#273 in d2473e5 and everything is working now.

• Dimmer close on cross button
• Dimmer is not repeated on interaction
• Scroll lock doesn't happen