Speed up incremental search reindex

[DavidMStraub]

The incremental search reindex was very inefficient in case of many updates. And that is what is used after importing a file. Imprting example.gramps locally using a SQLite index, before:

[2024-08-04 17:43:40,381: INFO/ForkPoolWorker-6] Task
gramps_webapi.api.tasks.import_file[48c173e5-0d0f-4cd6-b682-aef48bbdda9e]
succeeded in 2314.4943576940022s: None

... and after:

[2024-08-04 22:24:36,800: INFO/ForkPoolWorker-6] Task 
gramps_webapi.api.tasks.import_file[57839f70-15a8-4540-9d46-9d3e63f6d451]
succeeded in 77.58003538799676s: None

😮

I believe this fixes #436.

[DavidMStraub]

Added another fix: the search index wasn't updated after using the delete objects feature.