Kigo requests

[kkolotyuk]

Kigo and Kigo Legacy have different credentials but Kigo::LegacyRequest#builder creates Kigo::Request instance and passes there legacy's credentials. This credentials is not used inside the Kigo::Request but this is confusing situation.

Kigo::LegacyRequest#builder uses Kigo::Request as builder. My suggestion is to extract this builder in separate class and don't create Kigo::Request inside Kigo::LegacyRequest.

After this refactoring we could extract usage of Hanami.env from Kigo supplier as discussed #461 (review)