Refactor "Include templates"

The following discussions from !23495 (merged) should be addressed:

@grzesiek started a discussion: (+3 comments)

It is a little confusing that both params and context are hashes. Is there a way to have only one argument passed to this constructor somehow?
@grzesiek started a discussion: (+1 comment)

Is that a sign that we might need a separate class to handle location? Perhaps we can have enumerable Location? This looks like a code smell.
@grzesiek started a discussion: (+1 comment)

Overriding described_class this way might be an indication that our design needs some improvements. Is there a way to get rid of that override by tweaking params we are passing to the constructor?
@grzesiek started a discussion:

Why can't we just pass location?
@grzesiek started a discussion: (+2 comments)

Wouldn't it be easier to create FILE_CLASSES objects here with context? I find it quite confusing that we first normalize locations and then use select_first_matching. What is the benefit vs previous approach?

Edited Jan 07, 2019 by Grzegorz Bizon