Handle ElasticSearch character escaping

Prevent HTML escaping of ' to " in ESQuerySet templates and add a character escaping function. See https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-query-string-query.html#_reserved_characters

Not all cases are handled: searching for Brinkley\'s brings back a strange behavior (searches for Brinkley or s)

merged

mentioned in commit 58eddb09