Chnges for the issue where a recursive delete at space level destroys all apps. We ideally want apps to be soft deleted. We thought about various approaches, and decided to use the approach where we override the default destroy method of app.rb to do soft delete/ Now since we are retaining the apps after Space is deleted, we are making the apice_id column to be nullable, and ading checks to ensure that it is nullified only when space is deleted.