tmf: Make order of files processing more natural during import

tmf: Make order of files processing more natural during import

This changes the order of elements imported to be files first then
the folders, then by lexical order.

This makes it more predictable to the user when there can be name
clashes.

Bug: 500464
Change-Id: Iaf96c72a3fd9c9703ff9535f990a0092af75ff03
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/79986
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>