Implement Overlap queries

Summary:
Notes:

• Introduces the concept of queries on multiple properties (which meant changing query's internals a bit)
• Dates are stored as well as the "reference" in the index to allow quick filtering without fetching the whole entity
• Buckets are weeks starting on Monday (guaranteed by the use of the Julian calendar)
• Some size improvements are definitely possible (dates are padded numbers again, not using integer databases, Julian calendar starts at a very old date, etc.)

Test Plan: Tested in querytest

Reviewers: cmollekopf

Reviewed By: cmollekopf

Tags: Sink

Differential Revision: https://phabricator.kde.org/D13477