+ Credentials class keeping token and secret (e.g. username and password)
OauthTest: fixed namespace
Wconsumer UI: fixed ACP form for using new Credentials
HttpAuth fixed for using new Credentials
AuthInterface: removed formatCredentials() and formatServiceCredentials() b/c they are not needed now due to new Credentials
fixed errors in module install script related to new tables' schema definition

1. Fixed typo in 'wc_service_registry' table definition due to which no unique key was created on 'service' column
2. Remove redundant indexes on primary keys
ServiceBase: credentials getting/setting modified to reflect new credentials access way
Oauth refactored according to new credentials access style
Oauth2 fixes according to new credentials access style
HttpAuth::is_initialized slightly changes to use parent implementation
another bunch of changes related to new credentials access style
+ HttpAuth is_initilized() integration test
final changes per new credentials
fixed invalid class namespace reference
Merge branch 'feature/refactor-credentials-access' into feature/unit-testing
+ Authentication::__construct() test
Rest/Request fixes
another bunch of fixes: code style, phpdoc comments, etc
#48 AuthInterface: passing objects by reference is not needed