node/Tasks: merge improvements from PBS and make it more generic
this copies most of the task grid from pbs, but adds handling so that
users can add aribtrary filter fields
the filter fields always present are:
* since
* until
* task type
* task status
other filters fields can be added by giving an 'extraFilter' array
which must contain widget definitions that emit a 'change' event.
this is then used to update the filters for the api call
also you can add a 'preFilter' object, that sets the filter parameter
only once at the beginning