* Add some more checks to remove PHP warnings / notices.
* Adjust code to match CMS 9 API / interfaces.
* Do no longer use "query" but only searchTerm, as query is internal
API.
Use own service to handle data processing. Classes like indexer should
not know anything about the structure and how to process the data.
Also rename record to data, as we can process just any data in form of
an array.
Relates: #116