Honor translatable attribute for all types

This inspects the "translatable" tag for all message types and does
not add it to the catalog if it's set as false. This matches the
format specified in AOSP to indicate translatable strings.

android2po/convert.py

@@ -276,6 +276,10 @@ def read_xml(file, warnfunc=dummy_warn):
     for tag in doc.xpath('/resources/*[self::string or self::string-array or self::plurals]'):
         if not 'name' in tag.attrib:
             continue
+        if 'translatable' in tag.attrib:
+            translatable = tag.attrib['translatable']
+            if translatable == 'false':
+                continue
         name = tag.attrib['name']
         if name in result:
             warnfunc('Duplicate resource id found: %s, ignoring.' % name,