Issue #2323209 - Created a basic price field

I haven't add a price field instance to the commerce payment transaction because we don't have bundles yet, the price field storage is provided.
See https://www.drupal.org/node/2323209
We need to store amounts in a decimal(19,6) field, which maps to "type" => "numeric", "precision" => 19, "scale" => 6, in schema api.