Also logs when we try to create a view without a valid template key

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/angular/blob/master/DevelopmentWorkflow.md#running-the-tests
• Tests for the changes are included.

What is the current behavior?

What is the new behavior?

This fixes an edge case where if you set nsTemplateKey it won't create the default template, meaning not using a templateSelector will break the ListView.

Up to discussion: the previous integration would silently ignore missing keys and create the default template instead. Should we do the same, add a flag (fallbackToDefaultTemplate) or just do what this PR introduces (log as an error)?