Fix checkboxes on the nodes page

Checkboxes on the nodes pages behave incorrectly:
* The "select all" checkbox does not work
* The "Delete Nodes" button is enabled even if no checkboxes are checked

This patch fixes this by enabling preloading of tabs.

Change-Id: I5b725f8b80db5cb73e56b89165ba2a6df77d8f4e
Merge "Fix checkboxes on the nodes page"