LMDB implementation code copy/paste/modified into the Berkeley DB
implementation. Need to test if it builds, then if it works, and so on,
but the code is all there.
In order to make things more general, BlockchainDB now has get_db_name()
which should return a string with the "name" of that type of db.
This "name" will be the subfolder name that holds that db type's files
within the monero folder.
Small bugfix: blockchain_converter was not correctly appending this in
the prior hard-coded-string implementation of the subfolder data
directory concept.
Ostensibly janitorial work, but should be more relevant later down the
line. Things that depend on core cryptonote things (i.e.
cryptonote_core) don't necessarily depend on BlockchainDB and thus
have no need to have BlockchainDB baked in with them.
