Chage/alias 'start' to 'new'

#### Short description of the problem:
When you start a new project you will must write some like this:
`ionic start new_project blank --v2`

#### What behavior are you expecting?
You could use instead of 'start' the 'new' command? like this:
`ionic new new_project blank --v2`

#### Other projects use it as well:
**[Angular-CLI](https://github.com/angular/angular-cli#usage)**
ng new PROJECT_NAME

[**Symfony**](http://symfony.com/download)
`symfony new my_project`

**[Ember](https://github.com/ember-cli/ember-cli#usage)**
`ember new my-new-app`

You can keep the 'start' command and add as an alias the 'new'.

Start by locating the CLI registration and help text for the existing `ionic start` command. Add the requested `ionic new new_project blank --v2` alias while preserving `start`, then verify both command forms and their usage output.

索引モデルが issue の本文から書いたものです。