Consolidate the different "Plain C/C++" wizards somewhat.

We should not duplicate all wizard resources for every supported
build system -- this will not scale. Instead, have one top-level
directory for each type of wizard with build system specific data
in respective subdirectories and common data in another.
To support this approach, CustomWizard now traverses the template
directory recursively as long as no wizard specification has been found.

Change-Id: I8aad8cf36c5bf24d062f2d2c17fdb87ad12fd450
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>