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/Makefile.am

@@ -877,7 +877,6 @@ libbitcoinkernel_la_SOURCES = \
   init/common.cpp \
   key.cpp \
   logging.cpp \
-  netaddress.cpp \
   node/blockstorage.cpp \
   node/chainstate.cpp \
   node/coinstats.cpp \
@@ -906,11 +905,9 @@ libbitcoinkernel_la_SOURCES = \
   support/lockedpool.cpp \
   sync.cpp \
   threadinterrupt.cpp \
-  timedata.cpp \
   txdb.cpp \
   txmempool.cpp \
   uint256.cpp \
-  util/asmap.cpp \
   util/bytevectorhash.cpp \
   util/check.cpp \
   util/getuniquepath.cpp \