Add configuration page for active_shipping settings

The page shows up in the configuration tab and allows you to set all of the settings available in the extension.

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>

Fixes #47
Update Versionfile
Merge branch 'master' of https://github.com/spree/spree_active_shipping

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>

Conflicts:
	app/views/spree/admin/active_shipping_settings/edit.html.erb
	app/views/spree/admin/active_shipping_settings/show.html.erb