store addfile.logs in /STORE/logs dir outside collection repos

Instead of littering collection repos with addfile.log files
that slow down git-status whenever that is run, keep them all in
a log/ dir in the STORE.
tool for moving addfile.log files out of collection repos

This copies or moves all the addfile.log files out of a collection
into the /STORE/log dir and tars them up.
enable user to dismiss multiple tasks at a time

The next step is a "select all" button, followed by dismissable
alert boxes, but one thing at a time.
remove datetime objects from Celery tasks when dismissing

bc datetime objects are not serializable into JSON.
select-all button for task-dismiss list
refresh tasks-list page once per minute
refresh tasks-list more often; better messaging

- Refreshes every 30sec instead of every minute.
- Slight wording changes.
- Explanation if no tasks plus a "Back" button.
task_dismiss view for use in AJAXy task dismissal
TaskDismissForm now correctly handles empty tasks list

Formerly this would error out once there were no more tasks.
enable AJAX-y dismissal of celery tasks from inside alert box
Merge branch '172-task-dismiss-ui'
make dir for addfile log in log path func

Check for directory existence in the function that returns the
path rather than in the code that calls the function (so we don't
have to check for dir in multiple places).
Merge branch 'addfile-cleaner'
Merge branch 'master' into gitstatus-bkgnd