[Linux] Enhance GUI with icons

[tim-gromeyer]

Looks like this now

What doesn't work:

• Support for headphones without case and only 1 "pod", like Airpods Max (the backend currently doesn't support it as well)

What works:

• Auto hide case when battery is 0 and no airpod is in case
• Hide battery indicator when pod/case is diconnected
• Show battery level
• Show charging state (animated, Lightning symbol)
• Dynamic icon based on airpods model (currenntly only airpods 1-3, pro 1/2)
• Indicate ear detection status by changing opacity (will change this later)