New File Wizard: Fine tune selection of best node

If the user right clicked on a node and invoked the new dialog that way,
always consider that node even if it is deeper in the file system tree
than the new files.

Task-number: QTCREATORBUG-13215
Change-Id: Ic87033cb9a5e480eee8fb56eacad506d2fd39653
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>