Locate default json file according to XDG path

[strogiyotec]

Hey, I discovered ultralist recently and it's working for me much better than taskwarrior. The only thing I don't like is that it stores default storage file in my home directory. I would like it to be in my XDG_DATA_HOME directory. I checked the code and think it shouldn't be hard to implement .

1. Check file in current dir
2. Check file in XDG_DATA_HOME
3. Check file in home

If you are interested I will be glad co contribute