Accounting Entries can not be created before a contract start date
Moved logic from contracts model, added domain validations
Disallow accounting entries for closed contracts
Make termination of contracts compatible to new year ending logic
Add method to return all accounting entries for a given year
InterestCalculation can now be initialized with a year, removed need for annual_interest method
YearEndClosing now shows the essentials of what happened
added model to represent each years closing statement per contract
added todos from email to TODO.md