Improve getQuote GDPR error and add User-Agent

[joshuaulrich]

Yahoo Finance requires GDPR consent in some countries. We can't automatically consent for the user, so the data request fails with an ambiguous 404 error.

Yahoo also started to require a User-Agent in the header.

Fixes #392. Fixes #393.

[chartviewer]

Hi @joshuaulrich ,

I saw your fix and was quite excited to try it out. But still I am getting the GDPR error. Is there any other way to consent to the GDPR?

getQuote("AAPL")
Fehler in getQuote.yahoo(Symbols = "AAPL") :
Unbale to obtain yahoo crumb. If this is being called from a GDPR country, Yahoo requires GDPR consent, which cannot be scripted

Thanks!

[joshuaulrich]

It's not a fix. Ethan made the error more informative. Like I said in the issue, and in the commit comment, we don't know how to programmatically consent to GDPR. There may be a way to, but someone needs to figure it out.