migrate mmfile from libbitcoin to libbitcoin-blockchain
migrate history_database to just being a list of rows for outputs AND spends.
remove cruft from spend_db tool
rename history_database::add_row() to add_output()
history_row_id was renamed to point_ident
change history_scan_database to match fetch_history() semantics.
history_row_id renamed to point_ident: update tools and tests
update benchmarks to fix compile errors.
update database bucket values.
update fullnode example.
ability to activate the history database at certain heights.
add time to fullnode app
update validate endpoint.
Merge branch 'master' into version2

Conflicts:
	include/bitcoin/Makefile.am
	include/bitcoin/blockchain.hpp
	include/bitcoin/blockchain/blockchain_impl.hpp
	include/bitcoin/blockchain/database/history_database.hpp
	src/database/history_database.cpp
	src/impl/blockchain_impl.cpp