Flow query refactor

Better flow query refactor without HSTORE

replaces https://github.com/Tahi-project/tahi/pull/717
We removed the "My papers" default column because it the admin scope is this:

```
scope :admin,       -> { where(type: "StandardTasks::PaperAdminTask") }
```

Since we gave the ability for admins to create flows scoped to type, they can create their own flow that filters by `StandardTasks::PaperAdminTask`