Fix special functions order

[sebalaig]

• Do you want to request a feature or report a bug?
  Code cleanup

• What is the current behavior?
  In code, special functions are often written in the following order :

• Constructor
• Destructor
• Copy constructor
• Move constructor
• Copy assignment operator
• Move assignment operator

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem
  No

• What is the expected behavior?
  Special function should be in the following order:

• Constructor
• Copy constructor
• Move constructor
• Destructor
• Copy assignment operator
• Move assignment operator

• What is the motivation / use case for changing the behavior?
  Cleanup

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

(if a question doesn't apply, you can delete it)