Logger is now separated into its own module

Added eslint and fixed many logic errors based on its recommendations

backend/logger.js

@@ -0,0 +1,23 @@
+const winston = require('winston');
+
+let debugMode = process.env.YTDL_MODE === 'debug';
+
+const defaultFormat = winston.format.printf(({ level, message, label, timestamp }) => {
+    return `${timestamp} ${level.toUpperCase()}: ${message}`;
+});
+const logger = winston.createLogger({
+    level: 'info',
+    format: winston.format.combine(winston.format.timestamp(), defaultFormat),
+    defaultMeta: {},
+    transports: [
+      //
+      // - Write to all logs with level `info` and below to `combined.log`
+      // - Write all logs error (and below) to `error.log`.
+      //
+      new winston.transports.File({ filename: 'appdata/logs/error.log', level: 'error' }),
+      new winston.transports.File({ filename: 'appdata/logs/combined.log' }),
+      new winston.transports.Console({level: !debugMode ? 'info' : 'debug', name: 'console'})
+    ]
+});
+
+module.exports = logger;