Allow to filter by stock on some searchs

Now that we can indicate that the query of a SearchColumn needs to be on the
having part, we can transform some stock Columns to SearchColumns and it will
allow users to filter by stock, like: "Search for products with less than 5
units on stock", "Search for products with exactly 0 stock".

Change-Id: I6d7e59e7580bfc7b2a848d2de2f92c1d0e77c404
Fixes: http://bugs.async.com.br/show_bug.cgi?id=5338
Merge "Allow to filter by stock on some searchs"