Detect when the CLI is installed as a dependency and show an user-friendly error

[DimitarTachev]

Is your feature request related to a problem? Please describe.
It's easy to forget --global or --save-dev when installing/updating the NativeScript CLI. This leads to a strange fail in the native build of the app.

Describe the solution you'd like
The CLI could detect such cases and show an error describing the problematic state and possible solutions.

[edusperoni]

Maybe this should be treated like angular treats the cli? Make nativescript a dev dependency and the tns command will always check for a local version before running. This also prevents issues when working with multiple runtime versions (no need to keep switching the global package).

tns update/migrate would also update the cli.