contract view was in the CLI help but the command returned Not
implemented, and there was no owner API entry point for the existing
libwallet implementation. Add owner::contract_view through to the CLI
and the owner RPC, with a display for the result.
The slate is taken from --input or prompted for, as receive does.
is_executed was hardcoded to false. Derive it from our own tx log entry
for the slate, which is confirmed once the contract has executed.
wiesche