Should be able to edit times of jobs and shifts

[dcalacci]

When a user forgets to end a shift, it can be much longer than their real time working.

We should:

• allow users to edit the times of jobs and shifts manually
• ask users if the time of their shift is correct if any of the following is true:
  • The shift is more than 8 hours
  • The shift spans two days (overnight)
  • There is a large ( > 2 hr?) span of no jobs recorded in the shift.

[dcalacci]

We did the second in #82 , but haven't implemented job time edits yet.