Add 'type' param to ledger_data and ledger rpc commands (RIPD-1446):

The 'type' field allows the rpc client to specify what type of ledger
entries to retrieve. The available types are:

    "account"
    "amendments"
    "directory"
    "fee"
    "hashes"
    "offer"
    "signer_list"
    "state"
    "ticket"

src/ripple/rpc/impl/Status.cpp

@@ -23,6 +23,8 @@
 namespace ripple {
 namespace RPC {
 
+constexpr Status::Code Status::OK;
+
 std::string Status::codeString () const
 {
     if (!*this)