QnA question qualification optimizations

[csharpfritz]

The initial criteria for identifying a question for the bot to answer could be further optimized.

The Fritz.Chatbot\Commands\AzureQnACommand.cs CanExecute method is where this needs to be addressed

This method is tested in the Test\Chatbot\QuestionsCanBeAnswered.cs unit test fixture

• Text length + user name is longer than 10 characters, a better check is needed