Until now, `command_fail()` reported an error code of -1 for all uses.
This PR adds an `int code` parameter to `command_fail()`, requiring the
caller to explicitly include the error code.
This is part of #1464.
The majority of the calls are used during parameter validation and
their error code is now JSONRPC2_INVALID_PARAMS.
The rest of the calls report an error code of LIGHTNINGD, which I defined to
-1 in `jsonrpc_errors.h`. The intention here is that as we improve our error
reporting, all occurenaces of LIGHTNINGD will go away and we can eventually
remove it.
I also converted calls to `command_fail_detailed()` that took a `NULL` `data`
parameter to use the new `command_fail()`.
The only difference from an end user perspecive is that bad input errors that
used to be -1 will now be -32602 (JSONRPC2_INVALID_PARAMS).
