Allow CLType::Any as session args.

[zie1ony]

Often developers use their own structs with their own FromBytes implementation.
Then in smart contract code it is possible to write:

let arg: MyStruct = runtime::get_named_arg("arg");

Sadly it's not easy to construct such an argument with casper-client. There is a hack that can be used. Simply use an fix-sized array:

--session-arg "arg:byte_array_14='09000000536574506172616d7301'"

I'd like to able to write instead:

--session-arg "arg:any='09000000536574506172616d7301'"