Remove support for multiple databases

[gijzelaerr]

The support for multiple databases gets into the way a lot. 3rd party modules are hard to integrate and banana is hard to integrate as a 3rd party module. Also it introduces a lot of complexity infor example the middleware. In retrospect it makes much more sense to have a banana instance per database. We could also connect the banana version to the TraP database version.

Not sure if we are ever going to do this, but it would make Banana much more pretty and sustainable in the long run.