Fix warnings about signal-slot connection in filetree example.

Task-number: QTBUG-31079

Change-Id: I2696834f70bd0db05c9d70759b81159fabe561fd
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Add changes-5.1.0 file

Change-Id: I0d3ebb797ee1c185162a6defa4a58e2ffbfca41b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>