Add the capability to export GridCal model in plexel format (Excel sheet + datafiles)

[adrisanchu]

Add the capability to export GridCal model in plexel format (Excel sheet + datafiles).

Objective:

• Create an Excel file containing the Objects from the model as well as its Relationships
• Export profiles in .csv or .h5 format
• Pack everything into a .zip file

Steps:

• Create PlexelModel
• Create Plexel easy API (mapping Plexel - GridCal model)
• Add entry in the GUI saving dialog