Add `--save-args` flag to write new command defaults to dojorc

**Enhancement**

To enhance the dojorc defaults we could add a `--save-args` flag that writes new defaults to `dojorc`.
For example `dojo build -m dev --save-args` would save `mode: 'dev'` to the `dojorc` so that the next time you ran `dojo build` without args it would pick up the dev mode argument.