Add Mixxx e.V. to the Donations page

[JoergAtGithub]

No description provided.

[ronso0]

Then the Donate button(s) should also link to this new page
(currently it links to https://opencollective.com/mixxx)

And #422 should probably also relate/link to this.

[daschuer]

Looks good, thank you. I think we can make use of two orange buttons "Donate $" and "Donate €" to have an easy access, comming from other big donation buttons.
Without reading the wall of text.

[daschuer]

I have created JoergAtGithub#1
That removes the paypal reference and adds these buttons:

[daschuer]

In addition we need to adjust the redirect from the donation button in Mixxx itself:

content/_redirects:/donate https://www.opencollective.com/mixxx 302!

[ronso0]

Looks good.
However, the € and $ emojis look a bit strange on my end:

[daschuer]

However, the € and $ emojis look a bit strange on my end:

💶 The windows font looks better.

The advantage of the emojis is that they may be recognized.
Yes we can introduce our own symbols here but that's a bit of work, so lets postpone this.

[daschuer]

Let's start collecting €

Thank you for this PR.