Add /on NOTICE_GROUP and /fset NOTICE_GROUP analogous to MSG_GROUP

This hook and format are used for NOTICEs where the destination isn't
a channel and isn't yourself - eg. global targets like $$*.org.  This was
already the case for PRIVMSGs (using the MSG_GROUP hook and format).

Previously these were being routed like a normal NOTICE, and those don't
display the target, so it looked exactly like a private NOTICE to you.

This will also catch server notices sent before you're registered.

source/hook.c

@@ -153,6 +153,7 @@ HookFunc hook_functions[] =
 	{ "NICKNAME",		NULL,	2,	0,	0 },
 	{ "NOTE",		NULL,	3,	0,	0 },
 	{ "NOTICE",		NULL,	2,	0,	0 },
+	{ "NOTICE_GROUP",	NULL,	3,	0,	0 },
 	{ "NOTIFY",		NULL,	2,	0,	0 },
 	{ "NOTIFY_HEADER",	NULL,	2,	0,	0 },
 	{ "NOTIFY_SIGNOFF",	NULL,	1,	0,	0 },