Basic importing of products

This may not be the correct way to do things, but the base of this code comes from the pull request @deanperry started a little while back.

The imported fields are hardcoded for now, and they aren't comprehensive.

I've added localization support and had a go at the Polish and Brazliaian Portuguese ones myself – but they probably need someone who actually speaks those languages to have a look.

I've added an example format straight onto the importing page.  All localized as well.  Looks like this:

![File format example](https://dl.dropboxusercontent.com/u/47454402/example-format.png)

As you can see it also contains a bit of information about how the import works.

Lots of room for improvement but it's a start.
musi być w formacie csv, xls, lub xlsx