Fix typo in PREFERED_PROJECT_MODE

Replace PREFERED_PROJECT_NODE with PREFERRED_PROJECT_NODE.

This changes public API. The constant text does not seem to be stored
on disk anywhere, though ...

Change-Id: Id5393e597ed491b59075ff3687aaa4738fb3870c
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Fix 'prefered' typo in variable names

Change-Id: I15d65d4bb5a29b546b7a781051c3d641764d527e
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>