Usage of a odML template files

With the separation of more complex odML tree structures from the odML terminology side to a template store side (cf. #136) we could also provide a function that loads an odML file via an url or a local repository as an odML template:

```python
import odml

# returns the template odml file from the template store page (as clone)
doc1 = odml.load_template(url_some_temp_store_file)

# returns some local file (as clone) with the option to empty all values
doc2 = odml.load_template(dir_some_local_file, empty_values=True)
```