Rated items filter

[basvank]

Based on the discussion in #1 I'd like to propose this pull request.

The behavior of the filter is defined in the setting items.filter in the config file, which defaults to 'none'.

If items.filter=none, no filtering is done, so the algorithm behaves as before
If items.filter=user, all items are filtered from the candidate list which are already rated by the user in each and every context
If items.filter=user-context, all items are filtered from the candidate list which are already rated by the user in this particular context

Futhermore, I had to move around some files to get the build process and IntelliJ to work fine, as this did not work out of the box based on the project files. Therefore I created a build.xml file and altered the .gitignore such that the .iml and .idea/ files are not in the repo, so very contributor can use his own preferred IDE. I propose to do the same in the main repo, as 601bb14 broke everything for me due to the changes in the .idea folder. However, this is of course up to you.

[irecsys]

Thanks for your comments! Yes, I did not notice that when I committ them yesterday, I will take care of them once I got a second to do that. Too busy recently....lol