Add list of Cordova plugins to `ionic info`

Cordova plugins or their versions often cause problems for building apps or running apps on specific devices (with specific Android versions). It would help a lot if `ionic info` would also output a list of the installed Cordova plugins and their versions.

Examples where this would help to solve things:
- cordova-plugin-ionic-webview on Android <5
- console plugin still installed with cordova-ios 4.5.x

Start at the `ionic info` command and trace how it gathers the information it currently reports. Determine how installed Cordova plugins and their versions can be included, then verify the output with projects containing the example plugins described in the issue. Done means `ionic info` lists the installed plugins and versions clearly enough to aid build and device troubleshooting.

索引モデルが issue の本文から書いたものです。