create a simple sqlite database for Fluent

AppDelegate.swift

func configureDatabase() {
    let manager = FileManager.default
    let applicationDirectory = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
    let databasePath = applicationDirectory.first! + "/development.sqlite"
    if !manager.fileExists(atPath: databasePath) {
        manager.createFile(atPath: databasePath, contents: nil, attributes: nil)
    }
    let driver = try! SQLiteDriver(path: databasePath)
    self.database = Fluent.Database(driver)
}