Since the command to handler mappings are the most often modified and
referenced code in rpcserver.go and rpcwebsocket.go, move them near the
top of their respective files.
This commit cleans up the standard RPC command hanlding a bit by removing
the websocket specific notification channel from the handlers. This was
previously required because the sendrawtransaction, when called from a
websocket enabled connection, needs to add a notification for when the
transaction is mined.
This commit modifies that to instead implement a websocket extended
version of sendrawtransaction which invokes the standard handler and adds
the notification. In addition, the main send was modified to first look
if the command has a websocket specific handler first, and then falls back
to standard commands, rather than the previous approach of first checking
for a standard command and falling through to websocket commands. This
essentially allows websockets connections to extend commands with the same
name with additional functionality such as what was done in this commit.
The rpcserver.go file is starting to get a bit unwieldy. This commit
moves the separable websocket specific bits into a separate file named
rpcwebsocket.go.
