Add shareholders

[Obson]

When profits are distributed they can be shared equally (or otherwise) among employees (as bonuses) or they can be paid as dividends to shareholders. Or both. Introduce a new Shareholder class that receives a share of profits but not of wages in return for providing funds. Could be a subclass of Employee or merely an attribute of existing Employee class. Probably latter so they could raise funds as employees and invest them to become shareholders. Should be tied in with equality measurements.

[Obson]

Plan: Add virtual function Account::invest(int amount, Account *target). This will transfer amount to target's balance from caller (if available) and make a note in target of the investing account and amount invested. Investor also needs this info so it might be better for it to be held centrally in the Model instance rather than in investor or target.