Add "Donate" button to the About page

[katjost]

URL: https://www.flipcause.com/secure/cause_pdetails/MjMyMTIw

UI location:

(But please ensure the buttons are centered on the page)

Please ensure the link opens in a new browser tab.

[StubberG3]

@katjost This one's done, and it'll open in a new tab.