Support for params to be an observable

It was not possible to use observables for all validators, i.e. for the min rule. With this pull request the params object is first unwrapped before being passed to the validator method.

Only one test failed: Test 191, the error count in task-runner.htm as password and confirmPassword didn't raise an error. In my opinion this is correct as both values are undefined in the beginning. I added a required rule to confirmPassword to raise the required validation error.