Add unit test for the cleaning module

[leonardohscastilho]

Add unit test for the cleaning module with the following test cases:

• Empty entry list. It should return an empty list, too.
• List of transactions without internal references. It should left the list untouched
• A list containing two transactions with the same internal transfer reference. Since they have the same date but opposite amounts, they should be filtered from the return list.
• List containing two transactions with the same internal transfer reference but different dates, more than defined in BankProcessingTimeInDays. It should return the same list as the entry.
• List containing two transactions with the same internal transfer reference but one of them with 0 as the amount value. It should return the same list as the entry.
• List contains three transactions with the same internal transfer reference, two with the same amount value, and the other one with the opposite amount value. Should return a list with all these internal transfer reference transactions filtered.

[leonardohscastilho]

Refactor the test cases for better readability

Bugfix duplicated internal transfers:

• Now duplicated internal transfers will clean only pair of transactions. If one duplicated left, it will not get cleaned to not affect the final balance
• Test use case added to test this condition

Validate the simple transaction entries:

• Validate if the simple transaction field are valid
• Add a test case for testing this validation

@diegotsutsumi, you can check commit by commit to review it more easily.