fix: improve initial page of tns preview command

[Fatme]

Currently {N} CLI attaches on keyboard events and listens for pressing of specific keys.

• When a is pressed, {N} CLI shows the QR code of Playground app for android devices.
• When i is pressed, {N} CLI shows the QR code of Playground app for iOS devices.
• When c is pressed, {N} CLI shows the QR code for the application.

All this logic is removed as it is not user friendly.

Instead of this, {N} CLI shows only the QR code of the application and a message containing the download urls of Playground app in app stores.
Also a --link option is introduced - if provided only a url is shown on the console instead of QR code. This is useful when the user is not able to scan the QR code from terminal.

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

[Fatme]

run ci