XLS-Template import/export: use UUIDs instead of indicator names to match results

[okworx]

The mechanism of importing data using the XLS template export and import works pretty well. Only when the names of the indicators happen to be mixed up (see #43), trouble may be ahead, especially if instances of the Editor that are configured with different dataset languages are involved. Then some indicators may not be picked up correctly because the name differs in the XLS template and what the Editor expects.

One way to solve this could be to write the UUIDs of the indicators into the template as well and when importing, using these to match the results into dataset currently open.