Display error if user tries to send with priority fee without funds to pay for it

[deanpress]

Describe the solution you'd like and the expected behavior

If a user tries to make a transaction with a priority fee, but the user wallet holds no funds for said fee, the transaction dialogue closes on confirmation and nothing appears to happen.

For NEO blockchain transactions: Users should get a prompt to send without a priority fee if they don't have the funds (if a priority fee is configured).

For ETH transactions: Users should get an error.