Add ES field for year

Because we want to aggregate the data in ElasticSearch by year, a 'year'
field has been added to the mapping. This field will be filled using the
data in the Nederlab MySQL database.
Update ES mapping to include all fields in _all

Some fields were excluded from the _all field. Since it is not clear how
the _all field will be used, this restriction was removed.
Add ES fields for genre and subgenre data

Two fields were added to events, one to store genres and one to store
subgenres. We need this information, because we want to be able to
aggregate over them. Genres and subgenres are stored as tags
(non-analyzed strings).
Add script to save liwc categories + words to elasticsearch

Added a script that saves the liwc categories + their words to
elasticsearch. The liwc dictionary is saved in the type entitycategory,
with fields 'name', 'words'. This data is saved in order to be able to
get an overview of all words that belong to a certain category.