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

src/rpcclient.h

@@ -14,4 +14,12 @@ int CommandLineRPC(int argc, char *argv[]);
 
 json_spirit::Array RPCConvertValues(const std::string &strMethod, const std::vector<std::string> &strParams);
 
+/** Show help message for bitcoin-cli.
+ * The mainProgram argument is used to determine whether to show this message as main program
+ * (and include some common options) or as sub-header of another help message.
+ *
+ * @note the argument can be removed once bitcoin-cli functionality is removed from bitcoind
+ */
+std::string HelpMessageCli(bool mainProgram);
+
 #endif