make `/Search()` accented letters-insensitive

[paulhectork]

not really a problem, but it would be a nice feature to have an accents-insensitive search engine on /Search. right now, we get different results when searching for SEVIGNE SÉVIGNÉ Sévigné and sevigne.

we would just need to simplify the user's query and catalogue data before matching items in author_filtering(). there's aldready a function that does that: APP/utils/api_classes/match.py/compare(), which is used for the API.