Updating elda template

Elda files are based on a template that is subject to improvement and modifications. The template version is stored on the elda Status sheet. The current elda template is also stored in ELDA_TEMPLATE_VERSION. When reading an elda, the EldaVersionReader will compare the template version of the file to the current template version. In case of difference, the elda file will automatically be updated by update_elda_template().