Bugfix: clearSelection now also clears single selects

This release makes sure that the clearSelection method also clears the selection of single selects (using radio buttons) and not only multi selects (using checkboxes) which was the previous behaviour.

Support server-side-search

Adds a method that allows updating the dropdown options without rebuilding the entire widget. The rebuilding of the widget made the widget flicker and reset the search text every time.