Remove braintree dependency

https://github.com/spree/spree_gateway/pull/138/files#r10213250
Add braintree as a development dependency
Depend on Spree 2.3.0.beta
Bump to 2.3.0.beta
Correct email + homepage + files for gem
Removed savon dependency

Fixes #139
Use new preferences setter in AuthorizeNetCIM class
Correct arguments for BraintreeGateway's capture method
Remove BraintreeGateway#preferences

This is no longer needed with the recent preferences changes on Spree's master branch
Use new preferences references within braintree_gateway_spec to appease the testing gods
Remove ancient pending block for authorize+capture payment flow within BraintreeGateway's tests
Ignored options on BraintreeGateway#capture should be optional
Use correct options when calling capture in BraintreeGateway#capture tests
Braintree Credit test won't work because Braintree doesn't provide a way (yet) to settle the transactions
Set auto_capture to true before void tests + call right void_transaction method
Call correct credit! method in BraintreeGateway's spec's credit_using_spree_interface method
Added CARD_TYPE_MAPPING into StripeGateway to handle cases with Stripe.js passing in unexpected parameter mapping

Fixes #141
Added Mastercard Internet Gateway Service (Migs)

Fixes #144

Conflicts:
	lib/spree_gateway/engine.rb
fix capture arguments in StripeGateway

This now accepts the money, response_code and gateway_options as per Spree's own Payment::Processing code

Fixes #143
Add BraintreeGateway#cancel

This new method will decide whether to void or to refund a payment.

A payment can be voided if it's either authorized or submitted for settlement. In all other states, it MUST be refunded.

Fixes #145

Conflicts:
	app/models/spree/gateway/braintree_gateway.rb