buying singles? and improvements to buy album popup

[humancuration]

• logic, frontend/backend changes and options for purchasing singles
• rounding cents down (up?) to the decimal that makes sense for the current currency
• a gentle warning for accidentally huge amounts inputted (like, hey! that would be super generous of you, but are you really sure that this amount is correct? please double check!) or something if someone accidentally puts 500 instead of 5 for example. suggestions on the lower bounds for this to happen would be nice
• there is an space between the n and the k in the get download link email button 🐌