1) recalculate the offset, as ChromeDriver starts to follow the standard;
2) update screenshots;
3) correct the `click()` call with using coordinates, related to 1)
4) `sendkey()` with using key.modifier adjustment
5) add sleep
6) workaround for mastery failures
* Fix TestBench API imports, move functionality from custom elements
* Fixes to TestBench APIs and JavaDocs
* Merge remote-tracking branch 'origin/master' into 578_tbapi_cleanup
* Fix method name in CheckBoxGroupTest
* Remove unused custom element classes
* Implement getOptions using getOptionElements
* Replace setValue with setSelection in CheckBoxGroupElement
* Rename CheckBoxGroupElement getSelection to getValue
* Fix one last method
Move and rename server classes which go into the compatibility package
* Use com.vaadin.v7
* Use the same class name as in Vaadin 7
* Use a "vaadin7-" declarative prefix for Vaadin 7 components
Change-Id: I19a27f3835b18980b91a4f8f9464b2adde1a5fd5