Make date formats more consistent.

Try to follow:
- Months display as three-letter abbrev without "."
- Day of month without leading zero
- Time in the default format
- Input YYYY-mm-dd when humans might type it.(fields that use DatePicker use another format under the covers).

Ticket: #467
Branch: cleanup/467-date-format-consistency
Merge branch 'develop' into cleanup/467-date-format-consistency

Conflicts:
	timepiece/templates/timepiece/invoice/_weekly_entry_list.html
	timepiece/templates/timepiece/invoice/delete_entry.html
	timepiece/templates/timepiece/invoice/edit.html
	timepiece/templates/timepiece/invoice/list.html
	timepiece/templates/timepiece/user/timesheet/change.html
	timepiece/templates/timepiece/user/timesheet/view.html

Ticket: #467
Branch: cleanup/467-date-format-consistency
Merge branch 'develop' into cleanup/467-date-format-consistency

Branch: cleanup/467-date-format-consistency
Get tests running, fix a few more places

- Tests needed updating for the new date formats
- Tests revealed some more places in the code that needed updating
- Also found a few more in manual testing
- Also changed the format that DatePicker uses to yyyy-mm-dd, like everywhere else

Ticket: #467
Branch: cleanup/467-date-format-consistency
Merge pull request #467 from caktus/cleanup/467-date-format-consistency

Date format inconsistent across app