[themes] Add cycling for individual elements

Add functionality to provide lists of values for individual elements of
a theme (e.g. the prefix) and those will be cycled for each call.

This can be used, for example, to show a "charging" symbol for the
battery that continuously goes throw all the battery stages to "animate"
the charging icon.

bumblebee/modules/battery.py

@@ -28,5 +28,7 @@ class Module(bumblebee.module.Module):
                 return "discharging_high"
             return "discharging_full"
         else:
+            if self._capacity > 95:
+                return "charged"
             return "charging"
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