Add document types to the retention rules view layout

The type(s) of document(s) a retentionRule applies to is a very important info when looking at the file plan. In nuxeo-retention, the file plan is basically the nuxeo-retentionrules-view-layout layout, that displays a list of RetentionRules. Something like for example:

We need this column for our demos, and it is better off we don't have to override it every time.
Notice: I did deploy and test the modified layout and it works very well