refs #555 - Better display of negative times on dashboard
Factor out addition of css class name to negative times
Customizable negative time format
refs #518 - Use humanize time tags on Timesheet
Merge remote-tracking branch 'origin/develop' into 555-humanize-negative

Conflicts:
	timepiece/templates/timepiece/dashboard.html
	timepiece/templates/timepiece/user/timesheet/view.html
Merge pull request #702 from caktus/555-humanize-negative

Fixes #518, Fixes #555 - Better display of negative times on dashboard