Refactor ChargeCustomerWorker #1: Split #perform

As first step I've split #perform into multiple methods.
Refactor ChargeCustomerWorker #2: Moved private methods into services

I created service objects for charging customer, creating customer's token
marking charges as paid, notifications and errors. I also refactored exception
handling in app/workers/create_customer_token_worker.rb
Typo fixes, spec for MarkAsPaidService and autoload path update
Fix for wrong intendation in MarkChargeAsPaid spec
Merge pull request #23 from mtakac/master

ChargeCustomerWorker is hard to follow and not DRY. Refactor #20