Tidy up includes:

* Replace boost with std equivalents:
  - bind, ref, cref, function, placeholders
* More "include what you use"
* Remove unnecessary includes

src/ripple/peerfinder/impl/Manager.cpp

@@ -87,7 +87,7 @@ public:
     {
         m_queue.dispatch (
             m_context.wrap (
-                boost::bind (&Logic::addFixedPeer, &m_logic,
+                std::bind (&Logic::addFixedPeer, &m_logic,
                     name, addresses)));
     }