qtbase: fix cmake files to use our host binaries

* only for qt 5.1.0; didn't had the time to port this to 5.0.2
* client recipes need to export OE_QMAKE_PATH_EXTERNAL_HOST_BINS in EXTRA_OECMAKE

Signed-off-by: Simon Busch <morphis@gravedo.de>
classes: add new cmake_qt5 class

A cmake specific qt5 class which sets all required configuration parameters to
successfully compile cmake based applications.

Signed-off-by: Simon Busch <morphis@gravedo.de>