Electron update and Linux support

[GuillaumeDelorme]

No description provided.

[romainreignier]

Nice to see a PR for the Linux support, too bad it has not been merged yet.
We can still use the current version under Linux by copying a built PotreeConverter as libs/PotreeConverter2/PotreeConverter.exe.

I have also done a small patch that I was about to propose as a PR but this one is nicer.
Mine:

diff --git a/src/desktop.js b/src/desktop.js
index 1406c11..6d14299 100644
--- a/src/desktop.js
+++ b/src/desktop.js
@@ -1,4 +1,3 @@
-
 import * as THREE from "../libs/three.js/build/three.module.js"
 import JSON5 from "../libs/json5-2.1.3/json5.mjs";
 
@@ -82,7 +81,10 @@ export function convert_17(inputPaths, chosenPath, pointcloudName){
 
        const { spawn } = require('child_process');
 
-       let exe = './libs/PotreeConverter/PotreeConverter.exe';
+       let exe = './libs/PotreeConverter/PotreeConverter';
+       if(process.platform === 'win32'){
+               exe += '.exe';
+       }
        let parameters = [
                ...inputPaths,
                "-o", chosenPath,
@@ -179,7 +181,10 @@ export function convert_20(inputPaths, chosenPath, pointcloudName){
 
        const { spawn, fork, execFile } = require('child_process');
 
-       let exe = './libs/PotreeConverter2/PotreeConverter.exe';
+       let exe = './libs/PotreeConverter2/PotreeConverter';
+       if(process.platform === 'win32'){
+               exe += '.exe';
+       }
        let parameters = [
                ...inputPaths,
                "-o", chosenPath