These clauses filter the document space without affecting scoring and map to
Lucene's BooleanClause.Occur.FILTER. The `filtered` query is now deprecated and
```json
{
"filtered": {
"query": { //query },
"filter": { //filter }
}
}
```
should be replaced with
```json
{
"bool": {
"must": { //query },
"filter": { //filter }
}
}
```
This commit makes queries and filters parsed the same way using the
QueryParser abstraction. This allowed to remove duplicate code that we had
for similar queries/filters such as `range`, `prefix` or `term`.
