Provide JDBC folder in the hop folder to place user added JDBC drivers.

I use various JDBC drivers that do not come with HOP. It would be nice to have a JDBC folder in the main hop folder where I can easily copy a batch of my JDBC drivers into it to prepare connections for use.

Currently, every jar goes in hop/lib, and I frequently upgrade versions of hop and have to remember to capture each jar for the upgraded version of hop. This would be easier if a JDBC folder existed for this purpose and was in hop's classpath.