Rebroadcast unconfirmed transactions

[chill117]

It happens sometimes that transactions will sit in the mempool for a long time. Eventually these transactions are removed from the mempool and never confirm. To solve this problem, we can download and store the unconfirmed transaction (raw tx data) and store it with its payment request. Then, periodically, check to see if the transaction was confirmed (or lost from the mempool). If lost from the mempool, the app should rebroadcast the transaction.

https://github.com/bitpay/insight-api#transaction-broadcasting