Rails/WhereNot add table/column split

[mobilutz]

With this change, the cops suggestions and autocorrect splits a namespaces column reference into
table: { column: value }.

Example:

Comment.joins(:post).where.not('posts.title = ?', 'Title')

turns into ->

Comment.joins(:post).where.not(posts: { title: 'Title' })

PS: Almost the same as #406

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[koic]

Thanks!