Added eslint. To lint, npm run lint.

Linted the entire project. Using different rules for the script files
as there are a lot of undefined variables just because of the way the
DOM's global scope works.

Mostly just code cleanup, however the linter did catch a minor bug with
a settings regex. That has been corrected.

index.js

@@ -130,7 +130,7 @@ function getPlatformIcon(filename){
     return path.join(__dirname, 'app', 'assets', 'images', filename)
 }
 
-app.on('ready', createWindow);
+app.on('ready', createWindow)
 
 app.on('window-all-closed', () => {
     // On macOS it is common for applications and their menu bar