[users] Need <memory> for unique_ptr

- Although unique_ptr is only used when ICU is enabled, include it
  always because it is likely that we'll use more unique_ptr
  in the implementation at some point.

src/modules/users/Config.cpp

@@ -36,6 +36,8 @@ static const char TRANSLITERATOR_ID[] = "Russian-Latin/BGN;"
                                         "Latin-ASCII";
 #endif
 
+#include <memory>
+
 static const QRegExp USERNAME_RX( "^[a-z_][a-z0-9_-]*[$]?$" );
 static constexpr const int USERNAME_MAX_LENGTH = 31;