Add console/windows specification for Windows

Subsystem specification should be available for qbs.

On qmake this is achieved using CONFIG += console or CONFIG += windows

For g++, the following flags are configured in qmake.conf:

QMAKE_LFLAGS_CONSOLE	= -Wl,-subsystem,console
QMAKE_LFLAGS_WINDOWS	= -Wl,-subsystem,windows

For msvc it is:

QMAKE_LFLAGS_CONSOLE    = /SUBSYSTEM:CONSOLE
QMAKE_LFLAGS_WINDOWS    = /SUBSYSTEM:WINDOWS

This is related to QTCREATORBUG-7224