Accommodate URI scheme for LN invoice field when Withdrawing

[cointastical]

An LN invoice provided by some apps (e.g., BlueWallet) and services can come with the lightning: URI scheme. SN Withdraw does not recognize that and attempting to paste in the Invoice field an LN invoice with that will result in the flash error message: Error: could not decode invoice

See: https://docs.lightning.engineering/the-lightning-network/lightning-overview/understanding-lightning-invoices#uri-scheme

Example: lightning:lnbc20m1pvjlue[...]

So this request is for the Withdraw feature to accommodate a value in the Invoice field that includes an URI scheme (i.e., by stripping that out before attempting to decode the part that remains, the invoice).