Resources database backups
More and more things depend on KAMD's resources database. Recent documents, favourites, KRunner, to name a few. Now, SQLite is fairly stable with the write-ahead-log that has been enabled in KAMD for ages, but corruptions can still happen. Sometimes in SQLite, sometimes in the underlying file system. This patch introduces a two-step backup system for the resources database. On each start, the current database files are copied to `test-backup` directory. If no error appeared during the previous KAMD run, the `test-backup` files are promoted to `working-backup`. This means that in order for a specific version of the database to be considered as 'working' (promoted to a working backup), it needs to have been a beginning of an error-free KAMD session.
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