Restructure tutorial

[casella]

The current tutorial is organized in two sections:

• Library Architecture
• Examples

The first section goes very deep into the description of the library structure, which is interesting if you want to understand more and possibly develop your own models, but is definitely not necessary to start using the library. The tutorial should be restructured in three sections

• Using the Library
• Examples
• Library Architecture

where the first section provides an introduction to the drag-n-drop use of the library without getting into the details on how it is organized internally.

[AndreaBartolini]

As a reminder, the following arguments should be added:

• embedded power flow
  • overview
  • how to move the slack node to a generator node
  • auxiliary initial equations in the generator model to be used to compute external offset for PmPu and ufPu starting from the EPF
  • auxiliary initial equation in the ReferenceBus to be used to force to zero both the PSlack and the QSlack if the slack node is moved to another component
  • some examples (see PowerGrids.Electrical.Test.SynchronousMachine4WindingsPF)