Working billing address input on the checkout form

[PaitoAnderson]

The goal of this PR is to make it a bit easier for others to use this repo as a template to start their own store, by wiring up the billing address inputs which could be a big job.

• The only input on the checkout form that isn't captured is the newsletter, which could easily be done with an additional checkbox extra field.
• Basic form validation was added using required on inputs.
• Customer middle initial input was removed.
• Customer telephone input was added.
• @chec/commerce.js library bumped to latest.

[jaepass]

Thanks Paito! Will give this a test as soon as we can!

[PaitoAnderson]

Thanks @jaepass, great suggestions!