bitcoin-cli: remove unneeded dependencies (only code movement)

Remove unnecessary dependencies for bitcoin-cli
(leveldb, berkelydb, wallet, RPC server)

Build system changes:

• split libbitcoin.a into libbitcoin_common.a, libbitcoin_server.a and libbitcoin_cli.a

Code changes (movement only):

• split up HelpMessage into HelpMessage in init.cpp and HelpMessageCli in rpcclient.cpp
• move uiInterface from init.cpp to util.cpp