Fix audio preview still playing after closing the beatmap overlay
Fix case-sensitive linux build
Use IQueryable wherever possible
Fix write operations potentially using other-threaded tracked instances
Add missing database indices
Fix osu!direct panel load performance
Still needs to be async'd
No database-level where clauses were being used in many cases they should be.
Also add missing unique constraints where applicable.
Fix import after direct download being scheduled to update thread
Ensure all parsed "Online" IDs are above zero or null
Remove DatabaseBackedStore Prepare functions
Some .osu file sources (or database sources) may be in a bad state. We want to get these ones right as they cannot be enforced by the database itself (via FKs or constraints).
Caused a stall as experienced in #1364.