[start] - provide a helpful message when start with template fails for v2

[jbavari]

For v1 - when a start command fails with an invalid template, it shows the user a message to view templates.

Creating Ionic app in folder /Users/JoshBavari/Development/testing/v1 based on asdlfkj project
Downloading: https://github.com/driftyco/ionic-app-base/archive/master.zip
[=============================]  100%  0.0s
Downloading: https://github.com/driftyco/ionic-starter-asdlfkj/archive/master.zip
 ✗ Not found: https://github.com/driftyco/ionic-starter-asdlfkj/archive/master.zip (404)
 ✗ Please verify the url and try again.
Please verify you are using a valid URL or a valid ionic starter.
View available starter templates: `ionic templates`
More info available at: 
http://ionicframework.com/getting-started/
https://github.com/driftyco/ionic-cli

For v2 - we need a way to view templates. However, we do not want to show templates for v1 that are not available for v2.

[AwesomeZaidi]

I came here looking to find an aswer as well!