qml: use backend sighash check and add user confirmation path
qt: use backend sighash check and add user confirmation path
qml: include get_warning_for_risk_of_burning_coins_as_fees test in txdetails
qt: add warning icon to sighash warning
add sighash and fee checks to wallet.sign_transaction, making all warnings fatal unless ignore_warnings is set to True
tests: test sign_transaction on both code paths with ignore_warnings True and False,
raise specific exceptions TransactionPotentiallyDangerousException and TransactionDangerousException
7b96a83350