ES mappings: add aliases like author, keyword or title to make queries shorter

[egabancho]

[ludmilamarian]

For title we should check if title can only be one (remove the subtitle): based on ticket #1710 there are only 2 records using the subtitle: https://videos.cern.ch/search?page=1&size=21&q=exists:title.subtitle. Also, make sure to amend the search guide when this is done.