adds signature to card_stream_modern.rb and ports over some features of card_stream.rb
CRITICAL FIX: AVS fails for people with a flat number,
Remove CardStream legacy and replace it with CardStream Modern gateway
Fix CI

Exclude rails 23 + ruby 2.1.0 on tests
Only display travis status from master.
Merge pull request #1021 from Shopify/cardstream_signature

Cardstream P3 upgrade
Update CHANGELOG for 1.42.5 bump
Bump AM version to 1.42.5
Update few asserts in Conekta remote tests
Fixing up tests to ensure the changes are acceptable.
Update fixtures and fix one more test