Search end point improvements

Required for https://github.com/spiral-project/daybed.js/pull/28 to work 

* [x] Allow POST on search, because couldn't figure out how to set a body on a GET request with XMLHttpRequest
* [x] Prevent catching ES query syntax errors
I would expect this to be done inside the `search` method of the index rather than here, to keep the view file independent from elasticsearch.

Otherwise, we can define a SearchError exception that is to be used by the indexes?