Issue title: Feature Request: Editing Waypoints
 Issue body: When mapping out a path, you may want to alter or change a waypoint without clearing the entire list. Make the list selectable and re-populate the "Add" boxes with the selected values (change the "Add" button to "Update") and return to normal when the update is committed.
 Comments: 
 Comment 0: @bdaroz Thank you for the request. I really like the idea and will get that implemented within a few days. 
 Comment 1: @bdaroz I have added your requested feature. Thanks for the feedback!
{'source': 'GithubIssues', 'repo_name_with_owner': 'vannaka/Motion_Profile_Generator', 'issue_id': 283371197, 'repo_stars': 117.0}