Add option to use a local socket for QML debugging

Add option to use a local socket for QML debugging

Using a TCP debug server comes with a number of drawbacks. It has a
larger overhead than other connection types, the application has to
be able to access the network and there has to be an open port we can
find somehow.

Change-Id: Ia7fb24006b89419988c6504797303d84c3aa1bbc
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>