init comparisons

This MR initializes the core functions that will be called afterwards to perform the data compliance.

Layers' comparison

The list* functions allow to list the layers according to the type of format (folder with shp, gpkg, dxf)

To perform the comparison, like a diff file, we use the diff function which is based on Counter. We can then pass the lists returned by the 3 other methods and produce a result which will then be used to produce the log.

Fields' comparison

The fields will be compared with the compareFields function.

DXF2GPKG

I also added a utility function to convert a DXF to a GPKG. I'm surprised that this doesn't already exist in QGIS processing or that there isn't a plugin for this (I don't like how AnotherDXFImporter works)