Added comments to the gettext dictionaries generated by the xgettext tool.

The prefix to be searched for in the source code comments is TRN

CMakeLists.txt

@@ -321,7 +321,7 @@ include_directories(${GLEW_INCLUDE_DIRS})
 # l10n
 set(L10N_DIR "${SLIC3R_RESOURCES_DIR}/localization")
 add_custom_target(pot
-    COMMAND xgettext --keyword=L --from-code=UTF-8 --debug
+    COMMAND xgettext --keyword=L --add-comments=TRN --from-code=UTF-8 --debug
         -f "${L10N_DIR}/list.txt"
         -o "${L10N_DIR}/Slic3rPE.pot"
     WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}