[applets/batterymonitor] Improve UI for power management inhibition

This patch improves the UI for inhibiting power management and seeing
which apps are automatically doing it. Here are the changes, explained:

1. Use less jargonistic terminology for the feature itself, and remove
   the explanatory tooltip which is no longer necessary
2. Show the full list of apps which are inhibiting power management,
   because we have the space now that app icons are smaller
3. Correctly show and hide the list of inhibitions based on count and
   Whether or not the user has independently suppressed PM
4. Leave a bit more room for long reasons and alert translators to
   minimize string length as much as possible

BUG: 401108
FIXED-IN: 5.20.0