Add method to merge new params into an existent filter

Sometimes a filter is obtained from the database and it was previously configured with some params. Then, when the user uses that filter, sometimes it "adds" some params to the existent one, i.e: pagination params.

We need a method to merge these new params into the existent filter in an easy way. 

This is a very simple implementation of it. The decision to do it this way is to made it safe, because we reuse existent methods. The correct way is to implement the feature by it's own, but this gem have a messy code.