Setting icons at the widget level

[nyadiia]

Is your feature request related to a problem? Please describe.
The battery widget icon currently blends into my bar. I'd like to be able to change the icon(s) without changing the whole bar's icon theme.

Describe the solution you'd like
Some way to set an icon per widget, like how you're able to set a ramp in polybar or how you're able to set multiple icons in the format in waybar.

Describe alternatives you've considered
I could just switch the bar's icon theme however I would like to use a different theme per widget. Doing it with text as well ( like polybar and waybar ) would allow it to have the same color as the font for a more cohesive look.

[JakeStanger]

All icons should be customisable, ideally with support for both images and textual icons. This is inconsistent at the moment and I know I've made it worse with the introduction of the volume and notification modules. Because of that I'll look to address this as part of the next update.

[JakeStanger]

Moving this back to 0.16.0 because I've been working on a library to assist with both this and the upcoming sysinfo changes, so I think it makes sense to tackle both at once.

This will be towards the top of the pile in the next update.