(Gradle) JDBC driver should be provided by user

[grv87]

The common approach for similar plugins is to allow user to add a driver he wants as a dependency to a configuration. And use this configuration's classpath to run plugin's tasks. For example, Flyway accepts configuration names as an option. Another, simpler approach, is to create configuration (with predefined name) by plugin. User can add dependencies to this configuration, but can't choose another configuration.

Now the plugin downloads a bunch of drivers as dependencies which is neither necessary nor enough.