Enabling partial payment option for event registration and for online contribution pages

Schema changes (for both civicrm_event and civicrm_contribution_page)

• is_partial_payment, boolean (default = 0): controls if partial payments are allowed for this event
• initial_amount_label, varchar (255)
  NOTE: this was implemented as 'text', I changed to varchar
• min_initial_amount, decimal
• initial_amount_help_text, text

As per the attached image, add a new Checkbox widget to Configure Events >Fees tab, and to Configure Online Contribution Page, Amounts tab

• label = "Enable partial payment option?" (is_partial_payment) - unchecked by default

Add div with following fields. Div is hidden unless is_partial_payment is checked.
Initial Amount Label
Minimum Initial Amount ($0.00 or more).
Initial Amount Help

When Enable partial payment option? is checked, Initial Amount and Minimum Initial Amount are REQUIRED.

For Event > Fees, change the label background color new fields so they match other fields on the form.

On event registration (Register.php) and online contribution form (Main.php):

• Replace hard-coded "Record smaller initial amount" checkbox label with initial_payment_label, and fix layout so that checkbox aligns properly
• Display initial_amount_help below initial_amount field

Verify the min_initial_amount is validated against initial_amount value on form submit. If not, display error: "Your initial payment must be at least $min_initial_amount."
Verify that the amount actually paid is displayed on confirm and thank-you pages, and is displayed on receipt for both event reg and online contribution.
Also verify this flow for online contribution page with membership sign-up (quick config)
Verify DB state to expected results for a quick config partial payment:

• one line_item row
• one financial_item for the total amount owing, financial_account_id is the Income Account of the Financial Type associated with the event or online contribution page or the price set field or field value.
• two financial_trxn rows:

• one for amount actually paid (to_financial_account is "Asset Account of" the Financial Type associated with the payment processor used to make the payment)
• one for remaining amount owed (to_financial_account is "Accounts Receivable Account of" the associated Financial Type)