[ADD] account_taxcloud: Integrate TaxCloud API to get Sales Tax

- add a new checkbox on fiscal position: TaxCloud API
- when computing this fiscal position, it will:
        - return an existing tax if one exists for the same tax
          percentage, state, zip and TIC Category
        - or create and return this tax if it does not exists yet
- Create a data fiscal position: country U.S., tax cloud API
- In l10n_us, add a settings in accounting: compute tax automatically using tax cloud.

NB:
- The signature of map_tax has been modified to optionally specify the product
  and the partner on which the tax is applied
- The avoid the validationerrors that may occur while evaluation the tax with Taxcloud
  when a public user is on the frontend shop (website_sale), we have to execute the
  error silently by logging it.