[Feature] Better update handling of Plugins and Themes

[BLACK4585]

Before Requesting

• I found no existing issue matching my feature request
• This request is related to Millennium, and not a request for a specific theme/addon

Describe the feature you'd like!

It is very annoying that you always have to disable plugins or themes just to update them.
The flow is

1. Disable the Plugin/Theme
2. Restart Steam
3. Update the Plugin/Theme
4. Restart Steam
5. Enable the Plugin/Theme
6. Restart the Theme

This is so much effort. It would be nice if the updates could just be done in the background and get applied when Steam is restarted the next time.
A possible idea is that updates get just thrown into an update folder and Millennium first checks this folder at startup, applies the updates if available and then loads Steam.

Anything else?

No response

[BLACK4585]

Just saw that this is already the case for Themes. So my FR just applies to Plugins.