Updated package with PRs included

[stevenxxiu]

Hi everyone. I've been quite interested in using this extension. However the author appears to be inactive for quite a while on GitHub, and many useful PRs haven't been merged.

I've forked and tidied up this package myself at https://github.com/stevenxxiu/ColorPicker.

• I merged pretty much all the PRs here, and then re-wrote lots of the code, so it's cleaner after merging.
• Added code for alpha support.
• Ported the color picker to GTK4.

It's been tested on Linux and probably works on Mac.

My code uses PyGObject. I haven't tried installing this on Windows, and not too sure if it's directly included as a package in the Windows install of Python, or if it's run some other way. But anyone who wants to try and get it working on Windows and send instructions or a PR, is welcome.