New Event Registration with partial payment

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Summary
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Back-office staff may:

• Record partial payment for an event registration.
• Both the contribution and the participant record will be assigned a status of Partially Paid until the balance owing is zero. This will allow staff to easily locate partially paid registrations.

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Implementation
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1. Define new participant status: 'Partially paid'

• Status is 'Counted', Class='Positive', Reserved=TRUE, Visibility=Admin, Active=TRUE
• Add to civicrm_data
• Insert in upgrades

2. Define new contribution status: 'Partially paid'

• Reserved=TRUE, Active=TRUE
• Add to civicrm_data
• Insert in upgrades

3. New Event Registration (modifications)
Currently (4.4) the Total Amount (Payment Info field set) defaults to total owing AND the user can change that to a smaller amount. However we don't do anything special in that case. We need to make the following changes to postProcessing to handle this condition.

Client Side form behaviors (jQuery)
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• If user enters a Total Amount less than the calculated total fee, set Participant Status to 'Partially paid' (user MAY override this and change it to something else later)

• When user clicks "Save", if the Total Amount entered is less than calculated fees AND the participant status != 'Partially paid', put up a jScript confirm dialog:
  "Payment amount is less than the amount owed. Expected participant status is 'Partially paid'. Are you sure you want to set the participant status to $statusLabel? Click OK to continue, Cancel to change your entries."

Post Process changes
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• New contribution record is always inserted with the total OWING (calculated fees) as the total_amount. If total_amount = total owing, NO changes in the rest of the postProcess flow.

If the total_amount on the form is less than the amount owing:

• Contribution status is set to 'Partially paid'.
• Financial trxn record is created with total_amount = the amount actually being paid (total_amount from the form). Financial_trxn status is Completed. TO account = the applicable ASSET account (based in payment_instrument)
• A second financial_trxn record is created for the BALANCE owing. Rules for setting values for this transaction are the same as for a new Pending pay-later transaction:
• to_financial_account_id = account with "Accounts Receivable Account is" relationship to the financial type of the contribution
• from_financial_account_id = NULL
• status = Completed

• Line item records are created as usual.
• Financial item records are created for each line item as usual. Financial_item status = 'Partially paid'.
• Create civicrm_entity_financial_trxn records as per the base data flow: http://wiki.civicrm.org/confluence/display/CRM/CiviAccounts+4.3+Data+Flow#CiviAccounts4.3DataFlow-Offlinecompletedcontribution%28

Tests
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• Extend unit tests to cover participant create with partial payment
• Extend web-tests to cover the above workflow (participant registration with partial payment)