[core/theme] Fix detection of "best matching theme"

Previous code accepted the "first" hit in a theme - particularly, if a
module is called "A" and a *different* module "B" uses "A" as state, a
widget of module B with state A would be themed as *module* A, wrongly.

Essentially, made sure that the last (most specific) themeing "wins".

fixes #647

bumblebee_status/core/theme.py

@@ -35,8 +35,7 @@ def merge_replace(value, new_value, key):
     if not isinstance(value, dict):
         return new_value
     if isinstance(new_value, dict):
-        util.algorithm.merge(value, new_value)
-        return value
+        return util.algorithm.merge(new_value, value)
     # right now, merging needs explicit pango support :(
     if "pango" in value:
         value["pango"]["full_text"] = new_value