[Work in progress] Refactoring of all database stuff

While hacking on a pdo replacement for the current implementation of our orm I got the feeling that I was reinventing the wheel :) Therefore I stopped working on building our "custom orm thing" and replaced it with [propel 2](http://propelorm.org/).

Basically propel generates all the "basic" model code for us (stored in `app/models/Base` and `app/models/Map`). The generated code should not be stored in our repo, you have to generated it by running `vendor/bin/propel build --input-dir=config -vvv`. Propel uses a `schema.xml` for defining the database schema, which is used for the code generation. With this approach I could rebuild the models with propel very easy (and in nearly no time, I just had to write a few lines in the `schema.xml`).

I just need to update the controllers and this should be ready.

At this point I want to get some feedback before I will continue working on this.
@deleteman: Please look over the code and let me know if you are happy with my choice or if we should rethink :)