Better handling of digitization_correct field in XLSForm

[spwoodcock]

Describe the bug

Scenario 1: building does not exist

The user has to fill out the form currently, for a non-existant building.

Scenario 2: lumped building

The user cannot specify which part of the building they are mapping.

Scenario 3: split building

The user can mark the other building parts nearby as does not exist (map scenario 2), but should then able to draw the correct polygon

Expected behavior

Scenario 1:

The form should be completed immediately.

This flag will then inform the conflation step to delete the building.

Scenario 2:

The user should have an optional question to draw the part of the building they are mapping, or a text field comment to describe which part.

Scenario 3:

The user should have an optional question to draw around which buildings need to be grouped, or text field to describe.