Rename subject field to reason_text.

We were not using the subject field, so we will rename this to
reason_text, which will be used in future UI.

Change-Id: Ibe163446bde330c7840f86b7f94d27de31d59da9
Add image_label to DataCardImage.

Add optional image_label to DataCardImage. Set internal_id column to be
optional.

Change-Id: Ib01d3c44c2624d88388e1a5282bd60f2cb5b0507