Currently no way to clear a row in a Matrix question

[wmcclin]

In the Yap OUS (seasketch.org/fsm/surveys/430), there is a matrix question that asks respondents to estimate the percentage of catch used for various purposes. One of our facilitators accidentally selected an one radio butt for Sale and then realized the respondent doesn't actually sell their catch. So, they wanted to clear the row next to "Sale" but there's no means to do that. We could add a column for 0% but would it make more sense to have a button to clear the values?