centralized tags import/export into tags.py. Also added slo2eng and back as per 1088

src/export.py

@@ -1,4 +1,5 @@
 from browser import document
+from model.tags import export_tag
 
 
 def export_to_xml(model):
@@ -146,6 +147,8 @@ def export_translation(doc, translation):
 def _export_label_list(doc, lst):
     result = doc.createElement("labelList")
     for key, value in lst:
+        key, value = export_tag(key, value)
+        
         label_el = doc.createElement("label")
         label_el.textContent = value
         label_el.setAttribute('type', key)