feat(nodes): address feedback

- Address database feedback:
  - Remove all the extraneous tables. Only an `images` table now:
  - `image_type` and `image_category` are unrestricted strings. When creating images, the provided values are checked to ensure they are a valid type and category.
  - Add `updated_at` and `deleted_at` columns. `deleted_at` is currently unused.
  - Use SQLite's built-in timestamp features to populate these. Add a trigger to update `updated_at` when the row is updated. Currently no way to update a row.
  - Rename the `id` column in `images` to `image_name`
- Rename `ImageCategory.IMAGE` to `ImageCategory.GENERAL`
- Move all exceptions outside their base classes to make them more portable.
- Add `width` and `height` columns to the database. These store the actual dimensions of the image file, whereas the metadata's `width` and `height` refer to the respective generation parameters and are nullable.
- Make `deserialize_image_record` take a `dict` instead of `sqlite3.Row`
- Improve comments throughout
- Tidy up unused code/files and some minor organisation

invokeai/app/util/metaenum.py

@@ -0,0 +1,15 @@
+from enum import EnumMeta
+
+
+class MetaEnum(EnumMeta):
+    """Metaclass to support additional features in Enums.
+
+    - `in` operator support: `'value' in MyEnum -> bool`
+    """
+
+    def __contains__(cls, item):
+        try:
+            cls(item)
+        except ValueError:
+            return False
+        return True