Adding initial support for broadcasting transactions over Tor

- Support for ".onion" in --add-exclusive-node and --add-peer
  - Add --anonymizing-proxy for outbound Tor connections
  - Add --anonymous-inbounds for inbound Tor connections
  - Support for sharing ".onion" addresses over Tor connections
  - Support for broadcasting transactions received over RPC exclusively
    over Tor (else broadcast over public IP when Tor not enabled).

tests/unit_tests/CMakeLists.txt

@@ -62,6 +62,7 @@ set(unit_tests_sources
   mul_div.cpp
   multiexp.cpp
   multisig.cpp
+  net.cpp
   notify.cpp
   output_distribution.cpp
   parse_amount.cpp
@@ -100,6 +101,7 @@ target_link_libraries(unit_tests
     cryptonote_core
     blockchain_db
     rpc
+    net
     serialization
     wallet
     p2p