Takes care of proper special member generation globally, fixes #1689

Phew, a lot of classes were affected by this. The rationale for the
changes are as follows:

- When a type X declares any constructor, the default constructor is
  not declared, so there is no need for X() = delete there. In fact,
  there is brutal difference between those two: deleted members
  participate in overload resolution, but not-declared members do not!

- When a type X wants to be non-copyable (e.g. to be only movable, like
  threads, unique_ptrs, and so on), you can either do it by inheriting
  from boost::noncopyable (the old way), or better declare both (!) the
  copy constructor _and_ the copy assignment operator as deleted:

      X(X const&) = delete;
      X& operator=(X const&) = delete;

  We had tons of types with deleted copy constructors that were lacking
  a corresponding deleted copy assignment operator, making them still
  copyable and you wouldn't even notice (read: scary)!

References:

- http://accu.org/content/conf2014/Howard_Hinnant_Accu_2014.pdf
- http://www.boost.org/doc/libs/master/libs/core/doc/html/core/noncopyable.html

Note: I know, I'm quoting Hinnant's extraordinary slides a lot, but
getting the sematic right here is so incredibly important.

include/server/connection.hpp

@@ -39,7 +39,7 @@ class Connection : public std::enable_shared_from_this<Connection>
   public:
     explicit Connection(boost::asio::io_service &io_service, RequestHandler &handler);
     Connection(const Connection &) = delete;
-    Connection() = delete;
+    Connection &operator=(const Connection &) = delete;
 
     boost::asio::ip::tcp::socket &socket();
 

include/server/request_handler.hpp

@@ -28,6 +28,7 @@ class RequestHandler
 
     RequestHandler();
     RequestHandler(const RequestHandler &) = delete;
+    RequestHandler &operator=(const RequestHandler &) = delete;
 
     void handle_request(const http::request &current_request, http::reply &current_reply);
     void RegisterRoutingMachine(OSRM *osrm);