Bug 1086950 - donate home page promo

Bug 1094494 - donate link in top nav

DO NOT MERGE. We're still awaiting the URLs for the donate links (both the promo and the navbar) but should be able to review everything else.
Ah, right you are. Updated. 

Also, unless the string "Donate" is already in home/index.lang or main.lang we also need to wrap the nav link in a tag. I've done that now but we can remove it if that string already exists.