ui: MainView/NavigationTree: improve tree selection handling

ui: MainView/NavigationTree: improve tree selection handling

this fixes some bugs related to selection handling in the treelist:
* datastores were not selected after a reload
* reloading when in a tabpanel on any tab but the first, would
  not select a treenode
* changing between datastores on any tab but the first would
  not select the same tab on the new datastore

fixed those by mostly rewriting the changePath handling for
datastores and tabpanels in general

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>