Indexing the guest_token column on spree_orders

Closes #5648
Add .rubocop.yml

This is the default Hound ruby style config taken from:
https://github.com/thoughtbot/hound/blob/1f03cb64743765801a81c0f7ca9df64a448f1d48/config/style_guides/ruby.yml

These are the checks that Hound currently runs on every pull request.
This config allows people to run rubocop on their local boxes to see
what Hound is going to complain about when they push code.

Closes #5649
add rubocop to the common spree test and development dependencies.
add bullet to the sandbox Gemfile
point houndCI to our local rubocop.yml
set max line lenght to 100
prefer single quotes.
disable string literals, to much noise here.
Namespace eligibility validator like the rest.
fix spec
Remove old file.
Moving the default options[:lock] configuration into find_order_by_token_or_user so it can be used by both simple_current_order and current_order

Set simple_current_order to an empty order in case it's not found to avoid hitting the database needlessly

Using double quotes

Fixes #5647

Conflicts:
	core/lib/spree/core/controller_helpers/order.rb
Prevent admins from editing return items that have a processed exchange

Show return authorization return item preferred_reimbursement_type

When item isn't editable

Fixes #5651
Added reimbursed scope.

Fixes #5653
Update default same product rule

Changes:

- allows the SameProduct rule to exchange an item for the same item
- filters out out-of-stock variants for the SameProduct rule

Fixes #5652
fix api orders_controller_spec

Zipcode validation was failing in our fork because we have extra validation and the country didn't match up in these.
Also, remove some unused rspec address definitions.

fixes #5654
Bump version.
Bump beta.
Spree 3 & a new shiny ruby requirement as 1.9.3 security patches end of life soon.
Make ruby 2.0 syntax higher priority.
[API] add stores to the REST API
Fixes #5627
Were using circle ci.