Fix issue #190 and #195

This resolves issues where an integer column would raise an exception when handled by Ransack::Constants.escape_wildcards.

## Tests
I also created a shared example for wildcard escaping and included this example in the **cont** and **not_cont** predicate. I aliased `it_should_behave_like` into `it_has_behavior` because it reads better in the spec.

I ran all tests before submitting this pull request and they all passed.