Initial implementation

Features:

- [x] `loopback:app`
- [x] `loopback:model`
- [x] `loopback:datasource`
- [x] `loopback:acl`
- [ ] `loopback:model:property` - add a new model property, should be (repeatedly) called from `loopback:model`.

/to @ritch Please review. If you manage to approve this PR before I have time to implement the property generator, then I'll send the implementation in a new pull request. Otherwise I'll update this one later.
/cc @sam-github 

Depends on strongloop/loopback-workspace#46 and moll/js-must#16.