Edit contribution and change status to Cancelled or Refunded

I've updated the data flow wiki doc to reflect that we can allow either completed contributions to be updated to either Cancelled or Refunded. The book-keeping transactions SHOULD be the same, except that the contribution and financial_trxn status is set to either Cancelled or Refunded depending on status selected by the user.

http://wiki.civicrm.org/confluence/display/CRM/CiviAccounts+4.3+Data+Flow#CiviAccounts4.3DataFlow-RefundORCancelaCompletedcontribution(changestatustoRefundedorCancelled)

Several fixes are needed for this workflow:

1. When I Cancel a contribution, the newly inserted financial_trxn and financial_item amounts are positive, should be negative (this is already correct for Refunded status).

2. We should collect and store cancel_date and cancel_reason for both Cancelled AND Refunded contributions.
2.1 Update fieldset legend and field labels:
'Cancellation Information' => 'Cancellation or Refund Information'
'Cancelled Date' => 'Cancelled / Refunded Date'
'Cancellation Reason' => 'Cancellation / Refund Reason'

2.2 Modify jScript on contribution edit form so that cancelInfo row with cancel_date cancel_reason fields are exposed for either Cancelled OR Refunded status

2.3 Ensure postProcess records field values for these fields if user enters values for a Refunded contribution.

2.4 Update field labels on contribution view page.