[Refactor] Add Collectable class

[yellowbean]

From point view of SPV

As opposed to "Payable", there are couple components that can yield cash to the SPV

• Pool -> pool proceeds
• Hedges( Swaps )
• Accounts -> interests

What to collect ?

The income cash shall be tagged . it's a "Recovery" or a "Principal" or "Account Interest" ?

Statues Change

1. Accrue

• timestamp an accrue date, create the "cash" available to be collected

3. Collect

• collect the cash and mark the "collect date"
• remove the "cash" available component

Settle-able

if a type is Collectable meanwhile it is Payable
Then it shall be a new class called Settle-able which has a netting method