Widgetastic.core

Updates to Table widget handling with rowspan, fix for header locator

Update to the FillStrategy to include a context, so that conditional views which update the widget_names can be filled correctly.

Adding FillStrategy enhancement from izapolsk that allows for more fine-grained control of `View.fill` without consumers having to re-implement it.

Includes restoration of the 'exception' kwarg in wait_for_element, with the default behavior of the function unmodified. This is in order to support some implementation styles using this browser plugin method.

Modifications to `Browser.wait_for_element` that remove the ambiguous 'exception' kwarg, and modify method behavior to be more predictable as a 'wait' type method.