Fixed possible name resolution problem.

It is not safe to have settings partial called _settings, as soon as different plugin can have the same with the same name and one of them will not be loaded and will be replaced by another due to rails path resolution.
I think that #33 issue will be fixed by this patch (because helper code is now hidden inside a module and this will prevent autoloading from picking another SearchIssuesHelper instead of didyoumen-related one)
And ActionDispatch::Callbacks.to_prepare will keep patches from being unloaded in development.