Write statements with their qualifiers into the cirrus search index
Each statement should be stored without qualifiers, and then separately with each qualifier
For example, on wikidata the Mona Lisa has the statement 'depicts woman' `P180=Q467` and the statement 'depicts sky' `P180=Q527` with the qualifiers 'applies to part background' `P518=Q13217555` and 'color green' `P462=Q3133`.
We propose to store these in `statement_keywords` as follows:
```
'statement_keywords' : [
'P180=Q467',
'P180=Q527',
'P180=Q527[P518=Q13217555]',
'P180=Q527[P462=Q3133]',
]
```
In this way the user will be able to search using the `haswbstatement` keyword. If they want to find items with 'depicts sky' then can search for `haswbstatement:P180=Q527`, where if they want to find items that depict a green sky they can search for `haswbstatement:P180=Q527[P462=Q3133]`