Updated assets structure for changes in Spree 2.2

Conflicts:
	app/assets/javascripts/spree/backend/spree_digital.js
	app/assets/javascripts/spree/frontend/spree_digital.js
	lib/generators/spree_digital/install/install_generator.rb
Merge branch 'asset_fix' of https://github.com/davekiss/spree_digital
Fix the specs.