CoreSpotlight file search implementation

[hosy]

As an user I want to search a document via iOS global search field Spotlight.
If the user enter a search string which is equal to a file in ownCloud app, the file will presented in the search result. This deep links directly to the file in the ownCloud App.

This can be done with CoreSpotlight:
https://developer.apple.com/documentation/corespotlight

The user needs an option to enable, disable file indexing for every Bookmarkwhich was added in ownCloud App for privacy reasons.