added click method to tree.py

I have created an abomination in tree.py. I deserve to be burned to death.

some light changes, so far it works

removed the abomination, added click()
added configuration button to /regions/taskbar/center.py; added
select_dropdown to page.py

added select_dropdown
added test_infra_template

renaming template now works

selection now works

adding template now works

the test is now done and works

some renaming done
added test_infra_pxe_server

some additional finishing touchés
added test_infra_refresh_pxe_server

removed sleep

now asserts for expected image names

removed some unuseful commented lines
added test_infra_management_systems

mngmnt systems -> add new now works
new waiting for refresh in test_infra_refresh_pxe_server