[core-v2.4.0-alpha.8, react-v2.2.3-alpha.5, vue-v2.1.3-alpha.6] : Feature - Preflight notification handling

[Adamj1232]

Description

Adds Pre-flight Notification functionality to deliver standard notifications along with preflight information by passing a PreflightNotificationOptions object to the preflightNotification action. This will return a a promise that resolves to the transaction hash or null Promise<string> | null.

Preflight event types include

• txRequest : Alert user there is a transaction request awaiting confirmation by their wallet
• txAwaitingApproval : A previous transaction is awaiting confirmation
• txConfirmReminder : Reminder to confirm a transaction to continue - configurable with the txApproveReminderTimeout property; defaults to 15 seconds
• nsfFail : The user has insufficient funds for transaction (requires gasPrice, estimateGas, balance, txDetails.value)
• txError : General transaction error (requires sendTransaction)
• txSendFail : The user rejected the transaction (requires sendTransaction)
• txUnderpriced : The gas price for the transaction is too low (requires sendTransaction)

interface PreflightNotificationOptions {
  sendTransaction?: () => Promise<string>
  estimateGas?: () => Promise<string>
  gasPrice?: () => Promise<string>
  balance?: string | number
  txDetails?: {
    value: string | number
    to?: string
    from?: string
  }
  txApproveReminderTimeout?: number // defaults to 15 seconds if not specified <confirmed default with Gustavo>
}

Checklist

• The version field in package.json is incremented following semantic versioning
• The box that allows repo maintainers to update this PR is checked
• I tested locally to make sure this feature/fix works
• This PR passes the Circle CI checks

[lnbc1QWFyb24]

Just a couple of comments, but otherwise looks pretty good 👍

[lnbc1QWFyb24]

Looks good 👍