feat: add migration to move old files to xdg directory

+ add db column for migration version
+ handle pre-init migrations
+ handle post-init migration

app/migrations/_preinit/move_to_xdg_folder.py

@@ -0,0 +1,49 @@
+"""
+This migration handles moving the config folder to the XDG standard location. 
+It also handles moving the userdata and the downloaded artist images to the new location.
+"""
+
+
+import os
+import shutil
+from app.settings import APP_DIR, USER_HOME_DIR
+from app.logger import log
+
+
+class MoveToXdgFolder:
+    version = 1
+    name = "MoveToXdgFolder"
+
+    @staticmethod
+    def migrate():
+        old_config_dir = os.path.join(USER_HOME_DIR, ".swing")
+        new_config_dir = APP_DIR
+
+        if not os.path.exists(old_config_dir):
+            log.info("No old config folder found. Skipping migration.")
+            return
+
+        log.info("Found old config folder: %s", old_config_dir)
+        old_imgs_dir = os.path.join(old_config_dir, "images")
+
+        # move images to new location
+        if os.path.exists(old_imgs_dir):
+            shutil.copytree(
+                old_imgs_dir,
+                os.path.join(new_config_dir, "images"),
+                copy_function=shutil.copy2,
+                dirs_exist_ok=True,
+            )
+
+        log.warn("Moved artist images to: %s", new_config_dir)
+
+        # move userdata.db to new location
+        userdata_db = os.path.join(old_config_dir, "userdata.db")
+        if os.path.exists(userdata_db):
+            shutil.copy2(userdata_db, new_config_dir)
+
+        log.warn("Moved userdata.db to: %s", new_config_dir)
+        log.warn("Migration complete. ✅")
+
+        # swing.db is not moved because the new code fixes bugs which require
+        # the whole database to be recreated anyway. (ie. the bug which caused duplicate album and artist color entries)