fix #755 Display issues for the aria tester on IE10

Replacing:
  aria.core.Browser.isIE9
by
  aria.core.Browser.isIE && aria.core.Browser.version >=9
and
  aria.core.Browser.isIE && !aria.core.Browser.isIE9
by
  aria.core.Browser.isIE && aria.core.Browser.version < 9
in CSS templates of the aria tester.
fix #765 Now possible to set the option value to an empty string.

Close #767.
feat #785 Updating Splitter widget skinnable properties

Adding border-radius and background-color.

Close #785