Added xdg-compliant path for Linux and macOS

Created config.py

Moved system path logic to config.py

zut_app/config.py

@@ -0,0 +1,19 @@
+import os
+import platform
+
+USER_HOME = os.path.expanduser("~")
+WINDOWS_PATH = "zutui" # probably should be in %AppData% or something, but I'm not sure, so I won't change it
+LINUX_PATH = ".config/zutui"
+
+def get_config_path():
+    system = platform.system()
+    if system == "Windows":
+        APP_DIR = os.path.join(USER_HOME, WINDOWS_PATH)
+    elif system in ["Linux", "Darwin"]:
+        APP_DIR = os.path.join(USER_HOME, LINUX_PATH)
+    else:
+        print(f"System {system} not supported, aborting...")
+        exit(1)
+    if not os.path.exists(APP_DIR):
+        os.makedirs(APP_DIR)
+    return APP_DIR