Migrate before_filter to before_action

After `Rails 5.1`

All *_filter methods are now called *_action:
These methods were actually already deprecated in Rails 5.0, and Rails 5.1 removes support for *_filter usage, so you should be using *_action.

Before:

```ruby
skip_before_filter :authenticate_user!
before_filter :authenticate_user!
after_filter :do_something
```
After:

```ruby
skip_before_action :authenticate_user!
before_action :authenticate_user!
after_action :do_something
```