Add ChainstateManager::m_adjusted_time_callback

This decouples validation.cpp from netaddress.cpp (transitively,
timedata.cpp, and asmap.cpp).

This is important for libbitcoinkernel as:

- There is no reason for the consensus engine to be coupled with
  netaddress, timedata, and asmap
- Users of libbitcoinkernel can now easily supply their own
  std::function that provides the adjusted time.

See the src/Makefile.am changes for some satisfying removals.

src/test/miner_tests.cpp

@@ -10,6 +10,7 @@
 #include <node/miner.h>
 #include <policy/policy.h>
 #include <script/standard.h>
+#include <timedata.h>
 #include <txmempool.h>
 #include <uint256.h>
 #include <util/strencodings.h>