Allow driver and dialect override from config

[rnentjes]

I like to use a wrapper (https://github.com/rnentjes/Simple-jdbc-statistics) around the jdbc driver when developing, but it fails because of the hardcoded jdbc string to driver and dialect mapping.

For me an option to add a driver and dialect would be enough. I will see if I can create a pull request for this.

The stacktrace I get:

Exception in thread "main" java.lang.IllegalStateException: Can't resolve dialect for connection: jdbc:stat:webServerPort=11111:jdbc:sqlite:data/fullstack.db
	at org.jetbrains.exposed.sql.Database$Companion.getDialectName(Database.kt:146)
	at org.jetbrains.exposed.sql.Database$Companion.connect(Database.kt:115)
	at org.jetbrains.exposed.sql.Database$Companion.connect$default(Database.kt:111)
	at nl.astraeus.FullstackKt.main(Fullstack.kt:56)
	at nl.astraeus.FullstackKt.main(Fullstack.kt)