adds work hours so one can start keeping track of the hours worked on
each story

future plans

- add hours worked from entries#show using AJAX updates
- report billable hours worked for a given day; compare with the time-in
  / time-out clock hours
- nest in routes as appropriate
- provide option to record notes anytime hours are updated for a story;
  make it an opt-in so the feature doesn't become annoying

adjusts relationship between work hours and notes

updates views to exclude note_id

adjusts incorrect associations