Spree pages cleanup

Render 404 when it can't find a page.

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>
Added in all of the spree_essential_blog code.

Still need to add tests.

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>
Got specs passing. Added specs for posts model.

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