add comments to import

[hcientist]

modify the script so that it would notice a column that holds comments for the given rubric item or submission as a whole and ensures those are entered. The post to canvas code already looks for a "comment" item in the dictionary that we create from the csv file, but in parsing the csv to create this dict we are not currently attempting to notice any comment columns

so basically decide on a column header name convention (perhaps <crit_id>_comments?) and have the parsing code look for it and update the docs