refactor: grunt -> gulp

Hey @kenhkan,

Now it seems to check all boxes in #2, so would you have a try with this and review code changes here :)
and how about that `compiler.jar`, it seems to be not appeared in original `gruntfile`, is it a legacy one?

also copy the checkbox here:

- [x] `duplo dev`
- [x] `duplo dev http` (start http server, default: `disabled`)
- [x] `duplo new`
- [x] `duplo watch`
- [x] `duplo build`
- [x] `duplo release patch`
- [x] `duplo release minor`
- [x] `duplo release majar`
- [x] exclude dependencies