Merge and optimize Wallet tests

Summary:

• Optimize wallet test for performance
• Remove redundant tests
• Add tests for wallet chargeback/refund/credit/debit

Test Plan: ./phpunit

Reviewers: #hkccp_developers, mollekopf

Reviewed By: #hkccp_developers, mollekopf

Subscribers: #hkccp_developers

Differential Revision: https://git.kolab.org/D4616