Upgrade yeoman-generator to latest

[bajtos]

Prerequisite: a fully working test suite, see #354 (done).

Update yeoman-generator to the latest version (^3.0.0 as of now).

Because we are migrating across multiple major versions, we may need to update our code to accommodate breaking changes. Special attention must be paid to model generator that's repeatedly invoking property generator, this scenario must be tested manually via yo loopback:model.

[jannyHou]

Here is a list of items to do/finished:

• Updated the acl generator to extend the latest yeoman generator class
• Updated the tests for acl generator to use yeoman-test
• Update loopback-cli to create the env from yeoman-environment, see PR feat: switch to yeoman-env loopback-cli#71
• Fix the help option
• Update all generators
  • app
  • bluemix
  • boot-script
  • datasource
  • export-api-def
  • middleware
  • model
  • oracle
  • property
  • relation
  • remote-method
  • soap
  • swagger
  • zosconnectee

Related PR:

• feat: switch to yeoman-env loopback-cli#71
• upgrade generators to use the latest yeoman-generator #363