Remove wirecard and update upstream, ex_money

[oyeb]

This is a major step towards v1.1.1 :tada: See the milestone for more.

Money protocol

• ExMoney now implements the Gringotts.Money protocol so we don't need to implement it for them (#169).
• Moreover, we no longer need to keep ex_money in our deps!
  • So we introduced a FakeMoney struct that is available in test env. Since it implements the protocol as well, it is useful in tests (all tests have been updated because of this).

Misc

Updated upstream dependencies, changed credo settings. Travis now builds on Elixir versions: 1.5.3 and 1.6.5

Cleanups

1. Wirecard module was in no shape to be used and does not meet the standard for this library and is hence removed. Given that it was unusable, there is no need to provide any deprecation period.
2. Remove annoying compile-time warnings (most from the wirecard module).

[codecov-io]

Codecov Report

Merging #170 into dev will increase coverage by 10.51%. The diff coverage is 77.77%.

@@             Coverage Diff             @@
##              dev     #170       +/-   ##
===========================================
+ Coverage   66.82%   77.33%   +10.51%     
===========================================
  Files          14       14               
  Lines         434      375       -59     
===========================================
  Hits          290      290               
+ Misses        144       85       -59

Impacted Files	Coverage Δ
lib/gringotts/gateways/global_collect.ex	100% <ø> (ø)	:arrow_up:
lib/gringotts.ex	100% <ø> (ø)	:arrow_up:
lib/gringotts/gateways/cams.ex	93.75% <ø> (ø)	:arrow_up:
lib/gringotts/gateways/trexle.ex	100% <ø> (ø)	:arrow_up:
lib/gringotts/gateways/monei.ex	97.95% <ø> (ø)	:arrow_up:
lib/gringotts/money.ex	0% <ø> (-70%)	:arrow_down:
lib/gringotts/gateways/authorize_net.ex	97.56% <ø> (ø)	:arrow_up:
lib/gringotts/gateways/paymill.ex	100% <ø> (ø)	:arrow_up:
lib/gringotts/gateways/stripe.ex	0% <0%> (ø)	:arrow_up:
test/support/fake_money.ex	87.5% <87.5%> (ø)
... and 1 more

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