Add Amazon eGift Card payment method

[chimp1984]

Implements: #1866

@ripcurlx Would be cool if we could get it in 1.5.0. I think its not very risky and might be a interesting payment option.

@m52go Could you have a look at the popup text?

portfolio.pending.step2_buyer.amazonGiftCard=Please purchase an Amazon eGift Card for {0} at your Amazon account and \
  use the BTC seller''s email or mobile number as receiver. \
  In case the trade amount exceeds the permitted amount send multiple cards.\n\n

portfolio.pending.step3_seller.amazonGiftCard=The buyer has sent you an Amazon eGift Card by email or by text \
  message to your mobile phone. Please redeem now the Amazon eGift Card at your Amazon account and once accepted \
  confirm the payment receipt.
  
payment.amazonGiftCard.info=To pay with Amazon eGift Card you need to purchase an Amazon eGift Card at your Amazon account and \
  use the BTC seller''s email or mobile nr. as receiver. Amazon send then an email or text message to the receiver. \
  Use the trade ID for the message field.\n\n\
  Amazon eGift Cards can only be redeemed by Amazon accounts with the same currency.\n\n\
  For more information visit the Amazon eGift Card webpage. [HYPERLINK:https://www.amazon.com/Amazon-1_US_Email-eGift-Card/dp/B004LLIKVU]

[ripcurlx]

utACK

Code looks fine - I'll do a test trade during release testing.

[m52go]

Text looks ok.

[ripcurlx]

Text looks ok.

Shouldn't it be "Amazon sends"?

[chimp1984]

Text looks ok.

Shouldn't it be "Amazon sends"?

Yes.

[chimp1984]

Fixed in #4827