Console API: Add console.assert

Console API: Add console.assert

console.assert tests if an expression is true. If it is false,
it writes a message to the console and prints the JavaScript
stack trace at that point.

Change-Id: I5487552cb8a947e1947914166834e0bdedba3354
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>