Local storage mode to track incomplete submissions/payments

[timotheeg]

In local storage, add a marker that a form submission and payment has been submitted and is ongoing. The marker can be deleted when the payment flow is complete.

If the form page is loaded while the marker is present and recent (recency specifications TBD), we can query FormSG's server to check the status of the submission, inform the user of the details, and ask the user if:

1. he/she is sure she wants to proceed to make a new submission
2. proceed to payment page if the submission was pending

Dependency

• Create dedicate payment page with unique url #5932

[amitogp]

Blocked by dedicated payment page.

[LinHuiqing]

Design work required for toasts in the case of incomplete stuff!

[KenLSM]

Design/UX Required:

• Showing of toast, when + where
• Dismissal of toast (to have a "x" or text or something brilliant)

Probable Copies Required:

• "You have a previous payment action here"
• "Forget me"

Eng constraints:

• Prompt to clear can show anywhere
• Saving/updating submissions in storage can only be done after user clicks Proceed to Pay as we will track the paymentId