Do not crash when adding a file to an existing project that finishes
parsing while the wizard is still open.

Make sure the Node that is passed into the wizard is still valid after
parsing. Provide more information to the wizard so that this can be
checked -- and to find the similar node in the new project tree.

Also avoid a crash when adding existing files.

Do not crash when project parsing finishes while the wizard
summary page is open.

Do not crash when the project gets closed while the summary page
is open.

Do not have the ProjectTree send signals about subTreeChanges if
the node that changed is not part of the ProjectTree. This avoids
an infinite loop when updating the combobox on the summary page.

Add a treeChanged signal to ProjectTree.

Task-number: QTCREATORBUG-18651
Change-Id: Iaed3d0d1f079c09e54389821a11bda596139f35c
Reviewed-by: Eike Ziller <eike.ziller@qt.io>