XLIFF: support resname/name attributes

Handle 'resname' (XLIFF 1.2) and 'name' (XLIFF 2) attributes of
translation units and show them, if present, instead of the 'id'
attribute as the item's ID. These are meant to be used for symbolic,
human-readable identifiers, so are the appropriate thing to expose.

See #752.

src/catalog_xliff.cpp

@@ -580,7 +580,9 @@ class XLIFF12CatalogItem : public XLIFFCatalogItem
         m_string = str::to_wx(extractor.extractedText);
 
         // TODO: switch to textual IDs in CatalogItem
-        std::string id = node.attribute("id").value();
+        std::string id = node.attribute("resname").value();
+        if (id.empty())
+            id = node.attribute("id").value();
         // some tools (e.g. Xcode, tool-id="com.apple.dt.xcode") use ID same as text
         if (!id.empty() && id != m_string)
             m_extractedComments.push_back("ID: " + str::to_wx(id));
@@ -757,7 +759,9 @@ class XLIFF2CatalogItem : public XLIFFCatalogItem
         m_string = str::to_wx(extractor.extractedText);
 
         // TODO: switch to textual IDs in CatalogItem
-        std::string id = unit().attribute("id").value();
+        std::string id = unit().attribute("name").value();
+        if (id.empty())
+            id = unit().attribute("id").value();
         // some tools (e.g. Xcode, tool-id="com.apple.dt.xcode") use ID same as text
         if (!id.empty() && id != m_string)
             m_extractedComments.push_back("ID: " + str::to_wx(id));