Add way to log "Type of Evidence"

[adricaswell]

Suggestion by Ilona: In addition to the comment box in Vulnerability and Spatial Vulnerability Questions, add a way to log the type of evidence used to support the response. Give users type of evidence options to select from (we will still need to decide what types are specified - but something along the lines of "Peer Reviewed Literature" and "Expert Knowledge"). This will promt/ensure that users record this information. Provide users with a selection menu in the form of a list or a dropdown (Sarah will have a better idea of what is possible). Find balance between adding functionality to the app without making the UI cluttered.