Improve usability of Phrequent "Stop Time" dialog
Summary:
Fixes T5848.
- Disallow tracking negative time.
- Preserve note if there's an error with the time selection.
- Show start time and duration.
- Slightly better error messages.
Test Plan: Started and stopped time. Tried to select future/negative ranges.
Reviewers: hach-que, btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T5848
Differential Revision: https://secure.phabricator.com/D10218