Support for multiple db-drivers

                           
|Q            |A          |
|---          |---        |
|Bug Fix?     |y          |
|New Feature? |y          |
|BC Breaks?   |n          |
|Deprecations?|n          |
|Tests Pass?  |y          |
|Fixed Tickets|GH-31 GH-33|
|License      |MIT        |
|Doc PR       |           |
                           

This adds support for using multiple db-drivers (one per user-system), and fixes some related bugs.