Fixes #8424 - Controller concerns are loaded twice

config/application.rb, we are adding the controller concerns twice
folder to autoload_paths
Fixes #4613 - Remove duplicate scoped search from taxonomies
Fixes #8425 - n+1 query on audits index

Audits index include users who performed actions, and these are being
called with n+1 queries. Fix should be as simple as providing the
users through the controller with an includes.
Refs #3809 - Remove useless assignments
Fixes #8405 - Filter :interfaces_attributes when calculating templates_used
Fixes #7908 - normalize mac before host get saved

For some reason we save host without running valdiations when we import
attributes from facts. Therefore we have to take care of mac
normalization by ourselves. We have to normalize it just after setting
new value because save can occure anytime.
Fixes #8426 - Move scoped search into concerns

Scoped search definitions can be cumbersome at times and don't really
define the business logic of a model. I think hiding them under the
carpet by moving most of the definitions to concerns (as we do with
    hostext) we can later on include would keep the code cleaner.

There are 3 or 4 models with just 1 scoped_search attribute I didn't
bother to move. Later commits that move them into concerns when they
become bigger can just reference this issue.