Improve dependencies between compilation units

[mathbagu]

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

• What is the current behavior?
  Sometimes, depending on the changes, almost whole project is rebuild after a change. I think there is some troubles in the dependencies between the different compilation units, specially with the template implementations.

It's really easy to have circular dependencies, because we have a lot of bidirectional links between our classes. I think some #include statement could be replaced by a forward declaration. We have to write a coding style about headers management.

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem
  Do a complete build
  Change the implementation of a template method
  Run the compilation again

  • if the method was a classic method, in a CPP, only this CPP would be compiled
  • a lot of CPP files would be compiled

• What is the expected behavior?
  The project have to be cleaned to be compiled faster.

• What is the motivation / use case for changing the behavior?
  Be more productive.

• 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)

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