Add support for UUID for files.

[stefanheimes]

I found a little problem with fileTree Widgets in the MCW and this attribute. The sql use for the value field a simple text type so all binary data would not be readable. So we have to checnge the binary data back to a string.

    /**
     * {@inheritdoc}
     */
    public function valueToWidget($varValue)
    {
        if (!is_array($varValue)) {
            return array();
        }

        $widgetValue = array();
        foreach ($varValue as $row) {
            foreach ($row as $col) {
                // We can't handle binary data so we have to replace it.
                if (Validator::isStringUuid($col['value'])) {
                    $col['value'] = StringUtil::uuidToBin($col['value']);
                }
                $widgetValue[$col['row']]['col_' . $col['col']] = $col['value'];
            }
        }

        return $widgetValue;
    }

    /**
     * {@inheritdoc}
     */
    public function widgetToValue($varValue, $itemId)
    {

        if (!is_array($varValue)) {
            return array();
        }

        $newValue = array();
        // Start row numerator at 0.
        $intRow = 0;
        foreach ($varValue as $k => $row) {
            foreach ($row as $kk => $col) {
                $kk = substr($kk, 4);

                // We cant handle binary data so we have to replace it back to string.
                if(Validator::isBinaryUuid($col)){
                    $col = StringUtil::binToUuid($col);
                }

                $newValue[$k][$kk]['value'] = $col;
                $newValue[$k][$kk]['col']   = $kk;
                $newValue[$k][$kk]['row']   = $intRow;
            }
            $intRow++;
        }

        return $newValue;
    }

[stefanheimes]

We have to check multiple files as well.

[discordier]

IMO ir would be better to check if the sub field type is file picker as your implementation now prevents using uuids entirely as it converts them to binary in all cases.