[L4] Handle dot notation in live validation. Fixes #287

This pull request fixes the issue where live validation does not work for nested fields, as described in issue #287.

Tests have been added to ensure that dot notation works, and also that bracket notation still works.  I only added the tests for the "required" rule, but I can duplicate the tests for all the other rules as well, if you'd like.

Let me know if I need to change anything.  Thanks!