tasklist-server: prototype.

TaskList server  is a clone of Calendar Server.

Current target is to feeda zim plugin (python) with EDS tasklist (thus
this server will likely migrate to the extension).

Twofolds are the roots: no python support for ecalendar anymore and out of
process interface to EDS.

NB: the interface of the GetTasks is experimental. I include due_time
and remove all_day fields compared to GetEvents from CalendarServer.