Added preliminary support for DSN. Refs #4396

@markstory @AD7six thoughts on moving this into a Trait within the Core namespace and also adding it to Cache and Log?

- [x] Cache
- [x] Database
- [x] Email
- [x] Log

It does if you only allow the class to be specified as a query argument. I'm looking forward to that as you could more easily reuse other connection strings from multiple apps