task: Integrate into office module

Since I am striving for closer connection between my task management, my
mail suite and my calendar appointments, it makes sense to unify all
'office' tasks into the single office module instead of keeping
taskwarrior outside of it.

office/.config/sh/env.d/taskwarrior-xdg.sh

@@ -0,0 +1,3 @@
+#!/usr/bin/env sh
+
+[ -d "$XDG_DATA_HOME/task/notes" ] || mkdir -p "$XDG_DATA_HOME/task/notes"