Add support for a logo-file on a store

Change-Id: I43269b80635a22eaaa94e6cb00a4cd8139f3a4ea

Fixes #41
Fix s3 support

So thaaaaats how it works.

Change-Id: Ic3d5314137766b2e3125efd050d39e4df8e1645f

Related to #41
Don't include spree gem in gemfile - it's already in the gemspec

Fixes #44
Rename global_controller_helpers.

It needs to end in _spec to run via rspec.

Related to #45
Add default_currency to Spree::Store.

This will allow a user to override the globally configured currency
on a store by store basis.

Related to #45
Add default currency to admin interface.

Related to #45
Use default currency if currency is blank.

Related to #45
Fix arel query.
Associate payment_methods and stores.

This will allow a spree installation to specify which payment methods
are used in which stores.

If a store has no payment methods associated with it, all available
payment methods are considered valid.  If a store has at least one
payment associated with it, then only associated available payment
methods are valid.

Fixes #47
Admin interface for setting payment methods.

If multiple payment methods are available, this will allow a user to
specify which payment methods are available on certain stores.

Fixes #47
Update PaymentMethod.available for display_on

Fixes #49
Add email store from if order is tied to store.

Previously it would assume the order was tied to a store
which could cause errors trying to perform an operation
on nil.

Fixes #48
Restrict shipping methods for a store.

This will allow an administrator to restrict which shipping methods
are available for each store.

If shipping methods is blank, then all are available.

Fixes #50
Fix query again...