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
Bump to Spree 1.3.2

Fixes #46
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.
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.