Transparent-background

* Add few more options for resolving issues https://github.com/plemeri/transparent-background/issues/70 https://github.com/plemeri/transparent-background/issues/78 https://github.com/plemeri/transparent-background/issues/81

* The default directory of config file is `~/.transparent-background/config.yaml` but other systems other than PC would struggle finding accessible home directory, so you can not use `TRANSPARENT_BACKGROUND_FILE_PATH` environment variable to avoid such issue. Thanks again [kwokster10](https://github.com/kwokster10) for this contribution.
* Minor bug fixed for GUI
* You may now can use custom mode by changing config file and adjust `threshold` option in GUI

Fix issue https://github.com/plemeri/transparent-background/issues/65.

Fixing some issues for GUI script.

transparent-background` now supports gui powered by `flet`. Please refer to readme for more details.

Migration from google drive to github release for downloading pre-trained checkpoints
* Due to instability of `gdown` module, we changed default download method to `wget`
* Please remove `config.yaml` from `$HOME/.transparent_background` folder before upgrading to this release.
* Also consider downloading checkpoint files from this release page if problem persists. Download and move `.pth` files to `$HOME/.transparent_background`.

**Full Changelog**: https://github.com/plemeri/transparent-background/compare/1.2.9...1.2.12