Working on watch-folder

Added chokidar to watch for folder changes; added folder-watcher;
passing state to delayedInit on main;  added default values for new
preferences; added “Auto add torrents” preference with its checkbox and
path selector; TODO: start/stop watching on preference change, start
watching on init, add dialog when trying to enable preference without a
torrents folder.

package.json

@@ -17,6 +17,7 @@
     "auto-launch": "^4.0.1",
     "bitfield": "^1.0.2",
     "capture-frame": "^1.0.0",
+    "chokidar": "^1.6.1",
     "chromecasts": "^1.8.0",
     "cp-file": "^4.0.1",
     "create-torrent": "^3.24.5",