V1.8.0 - improved layers!

This is a very small update which introduces a single important feature: now the layer are named!
Previously, when enabling the export of the elements on different layers, it was hard to find the wanted layer since they were only numbered.
Worsening the issue, the add-on were exporting a layer for every supported element, even if there were no element to export. Now only the required layers are exported.

A few other changes has been made under the hood: following the file format """documentation""" (xournalpp/xournalpp#2124 (comment)), unnecessary/deprecated tags have been removed from the exported file reducing the final output by a few bytes (it's not life changing, but why wasting precious hard drive space?).

Additional note:
I found the XOPP documentation by mistake while monitoring the state of XOZ, the new WIP file format of Xournal++.
XOZ should gradually introduce new features and improve loading/saving performance, which is amazing, but it's not trivial at all to make a port in TypeScript/JavaScript (the programming languages used to make add-ons).
You can find additional information here #19.

Full Changelog: V1.7.0...V1.8.0