Support historic time entry

[dchenbecker]

Sometimes if I forget to start a task, or if I forget to record a task entirely, it would be helpful to be able to either be able to adjust the task start time after I've completed it or to start logging the work and adjust the timestamp before I complete it.

[nuttycom]

There is back-end infrastructure to support some of this functionality (the "amend event" route) but it hasn't yet been integrated into the front end.