templates: new default for zapp.yaml help->args

The previous default for help->args was a pair of empty strings. For the
most part, this feature is not used and just creates extra
work/annoyance when creating new apps. Every time I create an app, I
need to change the help->args to []. That's the default now.
Merge pull request #199 from larsbutler/fix-zapp-yaml-default-help

templates: new default for zapp.yaml help->args