Support recommendations for non-string primitive features

[reckart]

Is your feature request related to a problem? Please describe. There are currently no recommenders that support non-string primitive features. And when trying to use an external recommender for such features, some functionalities like active learning break.

Describe the solution you'd like It should be possible to have recommenders for non-string primitive features (i.e. boolean, integer, float).

To do

• [x] boolean (string matcher)
• [x] boolean (active learning)
• [ ] integer (string matcher)
• [ ] integer (active learning)
• [ ] float (string matcher)
• [ ] float (active learning)