Raising ArgumentError exception on Ransack operations

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Currently, when something goes wrong with some of Ransack operations of Searching and Sorting, it raises an ArgumentError exception.

There is a sample on the docs:

Article.ransack(unknown_attr_eq: 'Ernie')
# ArgumentError (Invalid search term unknown_attr_eq)

I`m proposing here to change it to a custom error specific for Ransack operations because this error is a Ruby internal one specific for missing arguments on a method call.

Besides that, Ransack users will tend to rescue this error to render a response to the end user and it may lead us to a bad error supression.

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I myself would like to work on it = )

[scarroll32]

Please go ahead @dfmoreto !

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@scarroll32 I think it's done. I've opened the PR #1478 with the resolution = )