oauth: add constants; move groups to folders; add credentials model
Add NSString+URLEncoding; Add more error constants; Stub OAuth consumer and view controller; Added comments; Add DWOURLParameterFormatter; Stub first tests for rest client;
Add NSException+Dwolla with client and api conversion methods;  Fix some test messages; Implement a few DWORestClientTests; Additional comments and pragma marks
Test and implement get relative path with all parameters in DWORestClient; Added existing untested post code;
Minor refactoring; smaller methods; remove magic strings; rename some constants;
Added pragma marks to better organize tests; added post tests for DWORestClient; handle nil body in DWORestClient post; Handle nil convertResponse in DWORestClient get and post;
Merge pull request #2 from Dwolla/oauth

Merge in progress OAuth branch