Add a function that return the number of payees on the Repayment Manager contract

The current payess on Repayment Manager contract is a private state; thus, it's difficult to retrieve from the front end.

See here

Line 20 in 7faa591

address[] private _payees;

@djuanit0x It's actually been removed - we actually thought that we could use the fund event to get the list of lenders.

Line 132 in 6f9b8b6

emit Fund(msg.sender, amount);