Added wysiwyg editor to the activity description fields

[SpookyBoy99]

Implements #1125 and fixes #1124. It is not the most beautiful implementation but this was the most practical solution within the established ecosystem.

[SilasPeters]

Great initiative. Even ctrl-z works! After testing, here are some remarks:

1. I can't enter the s character in the description field.
2. As you might have seen on whatsapp, the 'copy to whatsapp' does not convert/filter the HTML properly to markdown

[SpookyBoy99]

Not being able to enter an s is probably a side effect from the PR #1095, it has some more issues unfortunately. The copy to WhatsApp filter I'll have to rewrite completely I'm afraid, probably using the Delta API from Quill. A quick solution for now however, would be to just copy the inner text which would just strip all the HTML.

[SilasPeters]

@SpookyBoy99 what are your intentions on this PR?

[SpookyBoy99]

It's not the greatest implementation of a WYSIWYG editor and the copy for WhatsApp functionality is pretty much broken. I am not sure if I have the time or will power to completely fix those issues, so I might just close this PR unless there is enough interest from the board.

[SilasPeters]

I guess the product owners have the final call here @olafboekholt @TobiasDeBruijn . I don't have any strong opinions on this PR.

[TobiasDeBruijn]

While definitely a nice to have, the copy for whatsapp feature is a must have. If you feel like it, please do implement! Though if you'd rather focus on other projects or issues, that is completely fine as well, then this PR can be closed.

[SpookyBoy99]

I'll see what I can do during the 14 hour bus ride this weekend, if I don't manage to get it working by then I will just close this PR