Cleaner visual interface for assessment tool missing value annotation

[alyssadai]

Since all the unique for a given column are presented to be annotated as missing on the same page, it would be helpful if all column values were visually grouped in some way (with a gap between columns, color-coded, etc.) to make it a bit easier to keep track of what column you are annotating.

TODO

• Figure out what visual elements are practical to highlight the visual separation between rows that belong to the same column
• propose the visual element (check off with someone else)
• implement this visual element (assuming the table will not be sortable)
• write a test for it

[surchs]

Two options I can see:

• have the "column" column span multiple rows: https://bootstrap-vue.org/docs/components/table#comp-ref-b-td-props
• see if we can use custom styling to add another color on top of the "striped" aspect of the row styling (e.g. light blue color) to do a meta-stripe (i.e. color on/off between columns)