Multi-battery issues in PowerStatus

[sarahemm]

The PowerStatus application has several issues handling multi-battery systems:

• Actual: Batteries which are "idle" (not charging nor discharging) are shown as "Battery unused" but with the charging lightning bolt icon.
• Expected: No charging icon, maybe a "paused" icon instead for this situation.

• Actual: When one battery runs low, low battery popups begin despite having other fully charged batteries.
• Expected: No battery alerts appear until the last battery is low.

• Actual: When a second battery runs low, two popups start appearing for each notification.
• Expected: Only one notification popup appears for any given level of battery low-ness.

• Actual: If a battery is removed, the removed one is listed as "Damaged battery", capacity of ~2^{32mW (~4.2MW, probably -1 internally), the percentage sticks at whatever it was before removal, and the charging lightning bolt appears.}
• Expected: Percentage should show 0, capacity and all other data should be removed, "damaged" should either say "not present" or perhaps "damaged or not present", and could show an X icon over the battery.

This was tested on a Lenovo ThinkPad T450s with one non-removable internal battery and one external hot-swappable battery.

[waddlesplash]

Fix for the first part merged in hrev58239.

[waddlesplash]

Second and third parts fixed in hrev58242.

[waddlesplash]

Fix for the last part merged in hrev58276. Thanks for contributing!