Adds ELO card type

[deedeelavinder]

This adds ELO bin ranges and ELO brand logic in general. ELO is in a
partnership with Discover and is part of the Discover Global Network.
Using the ELO BIN ranges before the Discover regex allows those cards
to be identified correctly.

It also adds elo as a supported cardtype for the Adyen gateway.

Unit Tests
27 tests, 132 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions,
0 notifications 100% passed

Remote Tests
45 tests, 122 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions,
0 notifications 100% passed

[prashcr]

Related question for maintainers:
Is it worth distinguishing card network vs card brand?

Current

brand? == discover includes Discover cards, PayPal cards, China UnionPay cards and Elo cards
diners_club, jcb are considered as different card brands, even though they're also on the Discover network.

We don't handle partnerships/co-branded cards well

Ideas

I think there are users like me who primarily care about which network the card is on. E.g. I want to make sure cards on the Discover network are sent to a suitable processor.

Typically in the case of co-branded cards and partnerships, the cards are designated to be processed on one of the networks in particular (e.g. Diners/Mastercard as Mastercard, China UnionPay/Discover as Discover, Visa/Dankort as Visa etc.)
https://en.wikipedia.org/wiki/Payment_card_number#Issuer_identification_number_(IIN)

We could break up the current Discover range into its constituent brands, and provide a separate network? method to check the card network. And then do the same for other known partnerships.