--seconds: test fixed, bug fixed

This commit is a showcase for why we need unit tests...
Bugfix: "timestat -e"

"timestat -e" always edited the first action file, which is a bug. Now it
edits the selected action file.
'-a' synonym to '--actionfile' added
--day option added
More date formats accepted: today, yesterday, mm-dd
'--until' defaults to 'today'
--verbose option added
'timestat show' prints sum too
TODO updated
Bugfix: --current showed seconds
seconds_to_hhmm: works with negative numbers