Adding mongoid support

I have reintroduced mongoid support. It is working ~~with the exception of the ```top_scored``` method~~ .

I have tested this completely with mongoid 3.1.5 and rails 3.2.15

I could not get the mongoid-dummy app to run for some reason, I might look into this later. 

<b>Todo</b>: update generators to work with mongoid projects.