fix #963 test.aria.widgets.form.autocomplete.samevalue.AutoComplete failed on IE 11

Close #950
fix #962 autoselect is called asynchronously after focus()

Fix required as test.aria.widgets.autoselect.programmatic.AutoSelect failed on IE 11,
as .focus() is asynchronous on this browser.

Close #950
feat #972 prefix URLs in CSS templates

This commit introduces the possibility to define a method to be used to prefix all the image urls inside css templates.