[core/theme] Fix retrieval of rotating theme values (e.g. battery)

When rotating theme values (e.g. the "charge" icon of the battery
module(s)), until now, the code just showed the raw list (because it
wasn't aware of the need to rotate).

core/theme.py

@@ -116,6 +116,12 @@ class Theme(object):
 
         if not type(value) in (list, dict):
             value = self.__keywords.get(value, value)
+
+        if isinstance(value, list):
+            key = '__{}-idx__'.format(key)
+            idx = widget.get(key, 0)
+            widget.set(key, (idx + 1) % len(value))
+            value = value[idx]
         self.__current[key] = value
         return value
 

doc/NOTES.md

@@ -35,3 +35,4 @@
 - themes: use colors to improve theme readability
 - brightness: read from CLI tools
 - input: use events?
+- themes: rotating icons (battery!)