Small Features to csvimport

Hey,

* added a couple features to the csv import. I added django signals to the app, to allow the model to custom format a row. So if its some row that the app cant figure out we can transform it if we know what it is. 

* added appconf to allow the app to be more customizable. Right now I am just using it to manually select which models I am allowing to import from a CSV. But can be used for other settings. If they do not choose it will return to the default behavior.

* I also removed the except all clause. And added it to spcifically to database problems. This way if the user creates a handler and it fails it should return back a relative message. Rather than passing on and not inserting the data. 

There is some minor clean up I did. Sorry. Hopefully I didnt hurt blame to much. 

Thanks for writing this! Saved me a bunch of time having to make this!