Use a 'natural' sort order for UILists

Pretty much only affects the Saves and Screenshots tabs. Instead of
save1.ess, save10.ess, save2.ess, etc., we now show save1.ess,
save2.ess, save10.ess, etc., similar to most file managers (most
prominently Windows Explorer).

Author: Infernio

Mopy/bash/balt.py

@@ -2002,7 +2002,7 @@ def _SortItems(self, col, reverse=False, items=None, sortSpecial=True):
         items = items if items is not None else self.data_store.keys()
         def key(k): # if key is None then keep it None else provide self
             k = self._sort_keys[k]
-            return k if k is None else partial(k, self)
+            return bolt.natural_key() if k is None else partial(k, self)
         defaultKey = key(self._default_sort_col)
         defSort = col == self._default_sort_col
         # always apply default sort

Mopy/bash/bolt.py

@@ -1926,6 +1926,20 @@ def loadFile(self, path, progress, lang=u'english'):
             deprint(u'Error loading string file:', path.stail, traceback=True)
             return
 
+#------------------------------------------------------------------------------
+_digit_re = re.compile(u'([0-9]+)')
+
+def natural_key():
+    """Returns a sort key for 'natural' sort order, i.e. similar to how most
+    file managers display it - a1.png, a2.png, a10.png. Can handle both strings
+    and paths. Inspired by
+    https://blog.codinghorror.com/sorting-for-humans-natural-sort-order/."""
+    def _to_cmp(sub_str):
+        """Helper function that prepares substrings for comparison."""
+        return int(sub_str) if sub_str.isdigit() else sub_str.lower()
+    return lambda curr_str: [_to_cmp(s) for s in
+                             _digit_re.split(u'%s' % curr_str)]
+
 # WryeText --------------------------------------------------------------------
 codebox = None
 class WryeText(object):