[TIMOB-25575] iOS: Consider peplacing PLDatabase library with more modern approach

We are using the PLDatabase library for all iOS-related Ti.Database tasks for a long time, but it become pretty old-fashioned the last years. These days, [FMDB](https://github.com/ccgus/fmdb) is the recommended layer between the C-based libsqlite-library and Objective-C / Swift. It is recommended in several books like Learning SQLite for iOS and iPhone Advanced Projects and has some obvious advantages: * Automatic retry handling * Own SQL-functions * Asynchronous transactions for improved performance in batch-operations * Migration mechanisms, using [FMDBMigrationManager](https://github.com/layerhq/FMDBMigrationManager) Alternatively, there is [GRDB.swift](https://github.com/groue/GRDB.swift) which could (technically) still be used in our Obj-C project, but doesn't seem to be too popular so far.