add support for adding upscalers in extensions
move LDSR, ScuNET and SwinIR to built-in extensions

Fix: `error: Your local changes to the following files would be overwritten by merge` when run `pull()` method,
because WSL2 Docker set 755 file permissions instead of 644, this results to the error.

Updated `Extension` class: replaced `pull()` with `fetch_and_reset_hard()` method.

Updated `apply_and_restart()` function: replaced `ext.pull()` with `ext.fetch_and_reset_hard()` function.

list changed Settings keys in UI
do not print VRAM/etc stats everywhere but in calls that use GPU

Fixed for "Available" tab

fix broken Restart Gradio button