Strip Empty/Blank Params from Ransack Params Hash

By letting key value pairs with the value being an empty string into the params hash, Ransack creates an SQL query that unnecessarily adds LEFT OUTER JOINs.  These unnecessary LEFT OUTER JOINs cause duplicate data to be returned from the database.

You can either accept this pull request, or use `.result(distinct: true)` in order to remove the duplicates.  The disadvantage of the `distinct: true` option is that it can cause a full table scan when one is not necessary, so with massive sets of data, this solution is preferred.

Includes 3 tests to back up changes as well.