Refactor projects controller a bit
Rename GetTransactionStatusRequest

Dropping the "Get" makes it more readable.
Extract a superclass for Amazon requests

BaseFpsRequest and BaseCbuiRequest had a lot in common.
Now, a lot of functionality (like signing) is handled in
Amazon::Request
Minor refactorings of outbound signature classes
Abstract another method into Amazon::Request
Get rid of pointless SignatureUtilsForOutbound methods
Refactor signature_utils_for_outbound
Lots of small refactorings
Add base class for responses from Amazon
Remove empty spec lib_helper file