web elem highlighting now configurable

Web element highlighting can be configured through
gwen.web.highlight.style setting.  Default value is "background: yellow;
border: 2px solid gold;".  Also radio and checkbox elements have their
parent highlighted if they are the sole input child element.
import cleanup
removed redundant 'text' literal from compare steps

No need to specify redundant text literal in steps that assert element
text
element highlighting fix