gets a click event handler for either scope filter buttons or kind filter buttons.
function getFilterClickHandler(filter) {
            var isKind = filter === 'kind';
            var has = isKind ? sbSearch.hasKind : sbSearch.hasScope;
            var add = isKind ? sbSearch.addKind : sbSearch.addScope;
            var remove = isKind ? sbSearch.removeKind : sbSearch.removeScope;

            return function (event) {
                var btn = $(this);
                // get scope or kind value from the data- attribute.
                // e.g. data-scope="instance" or data-kind="method"
                var value = (btn.attr('data-' + filter) || '*').toLowerCase();

                // if we already have this filter, we'll remove it
                if (has.call(sbSearch, value)) {
                    remove.call(sbSearch, value);
                } else if (event.shiftKey) {
                    // if shift is pressed, we'll add it (multiple filters, no
                    // duplicates)
                    add.call(sbSearch, value);
                } else {
                    // otherwise, we'll set it as the only filter (replace with
                    // previous)
                    sbSearch[filter] = [value];
                }

                var strSearch;
                if ($txtSearch) {
                    sbSearch.parseKeywords($txtSearch.val());
                    strSearch = sbSearch.toString();
                    $txtSearch.val(strSearch).focus();
                    if ($btnClean) $btnClean.show();
                } else {
                    sbSearch.keywords = [];
                    strSearch = sbSearch.toString();
                }
                filterSidebarNodes(strSearch);
            };
        }