Mink elements (including the document element) provide a
"find(selector, locator)" method to look for child elements in their web
browser session. The Locator class is added to be able to store the
selector and locator in a single object; it also provides a fluent API
to ease the definition of Mink locators, specially those using the
"named" selector.
The method "find(locator, timeout, timeoutStep)" is added to Actor
objects; it is simply a wrapper over Mink's "find(selector, locator)"
method, although it throws an exception if the element can not be found
instead of returning null, and it also makes possible to automatically
retry to find the element for certain amount of time.
Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>