add I.Check which returns a boolean

[lazytesting]

Currently we have 'Assert' which throws an exception when a check if failing.
It would be good to have a way to do the same assertions which are simply returning a boolean.

This way it's possible to use the assertions in the unit test framework. This way we can use WbTstr.Net in combination with SpecFlow in the following way:

• PageObject : private selectors, public methods to perform actions or checks. (so no actual validations here)
• StepDefinition: calling methods on page object, assertions based on unit test framework
• Features: actual test logic