Soft delete for airlines/flights

[nabeelio]

Use soft deletes for these when assets exist. There should be a field that's set when it's inactive. But have it exist outside of Eloquent because those assets won't be found, even if they're around.

Also, for a delete, check if it's in use and do the soft delete. Do the same model that is being done now for users for all of these assets (fares, etc)