Improving the functionality os the RSS feed.

#4319 

I applied the fixes: 
1. Set the pre defined feeds from node types to be on the top
2. news, blog, events, presentation, biblio are checked by default.

And only selected terms can be chosen by anon to create feeds.

![settings](https://f.cloud.github.com/assets/1222368/2511440/6cf20260-b418-11e3-8c4a-bf447dc0b7dd.png)
![view](https://f.cloud.github.com/assets/1222368/2511441/6d0dd7ba-b418-11e3-85cb-3f2cfe0d8a7a.png)

Only the terms the selected from the CP will be available for anon users.
![screenshot from 2014-03-25 14 26 42](https://f.cloud.github.com/assets/1222368/2511473/2778503a-b419-11e3-9c7a-37a96bbf9c7f.png)
![screenshot from 2014-03-25 14 26 51](https://f.cloud.github.com/assets/1222368/2511474/279df1be-b419-11e3-98b7-92d6f39f3304.png)
![screenshot from 2014-03-25 14 26 55](https://f.cloud.github.com/assets/1222368/2511475/27c1d282-b419-11e3-9bfc-0c7a4ad7bddb.png)