new wipeable_string class to replace std::string passphrases

src/common/password.h

@@ -32,6 +32,7 @@
 
 #include <string>
 #include <boost/optional/optional.hpp>
+#include "wipeable_string.h"
 
 namespace tools
 {
@@ -58,11 +59,10 @@ namespace tools
     password_container& operator=(const password_container&) = delete;
     password_container& operator=(password_container&&) = default;
 
-    const std::string& password() const noexcept { return m_password; }
+    const epee::wipeable_string &password() const noexcept { return m_password; }
 
   private:
-    //! TODO Custom allocator that locks to RAM?
-    std::string m_password;
+    epee::wipeable_string m_password;
   };
 
   struct login