feature(downloader.py): Add HTTP proxy support

[gyptazy]

General

DiffusionBee may fail to download models when running in a proxy environment where:

1. ENV vars can not be evaluated due to Electron
2. Custom proxy settings may be required in general
3. A dedicated proxy should be used

This PR adds a possibility to add a config file to DiffusionBee's dot dir (.diffusionbee/config.ini). By section, this may be extended for additional params in future. To define a proxy, just place:

[proxy]
host: http://localhost:8000

Why ini? While other files already are json I'd really like to prefer json but writing json is not beginner and human friendly. Therefore, I'd stick to ini.

Issue

Fixes #445

Ideas

This could also be added to the GUI in future to read/write settings.

[TIMESTICKING]

Hi, It doesn't work, still shows Error: please check your internet connection or firewall. read ECONNRESET.
Ive check the port, and replace the localhost with 127.0.0.1