Move CTxDestination to its own file

CTxDestination is really our internal representation of an address and
doesn't really have anything to do with standard script types, so move
them to their own file.

src/test/miniscript_tests.cpp

@@ -10,6 +10,7 @@
 #include <test/util/setup_common.h>
 #include <boost/test/unit_test.hpp>
 
+#include <addresstype.h>
 #include <core_io.h>
 #include <hash.h>
 #include <pubkey.h>