Position taskbar button

[Offerel]

This should reposition the taskbar button, according to the sorting in $config['plugins'] array. Please see #46

BTW: You can remove libcalendaring and other dependencies from this array, because they are loaded automatically by the already implemented:

protected function setup()
{
    $this->require_plugin('libcalendaring');
    $this->require_plugin('libkolab');