Currently we don't allow the user to view or edit the is_active flag for relationships. We should allow users to set this value so that relationships can be "disabled/deactivated" regardless of the presence of start and end dates.
1. Add "Enabled" checkbox to Create/Edit relationships form. Default is "checked" on add.
2. Add "Enabled" field to View relationship.
3. Contact View - Relationships tab: Modify title of "lower" selector from "Past Relationships" to "Inactive Relationships". Modify desciptive text as well ("These relationships are Disabled OR have a past End Date."). Modify query if necessary to filter on either a past End Date OR is_active flag = 0.